Showing papers on "Extinction ratio published in 2018"

Graphene-silicon phase modulators with gigahertz bandwidth

Abstract: The modulator is a key component in optical communications. Several graphene-based amplitude modulators have been reported based on electro-absorption. However, graphene phase modulators (GPMs) are necessary for functions such as applying complex modulation formats or making switches or phased arrays. Here, we present a 10 Gb s–1 GPM integrated in a Mach–Zehnder interferometer configuration. This is a compact device based on a graphene-insulator–silicon capacitor, with a phase-shifter length of 300 μm and extinction ratio of 35 dB. The GPM has a modulation efficiency of 0.28 V cm at 1,550 nm. It has 5 GHz electro-optical bandwidth and operates at 10 Gb s–1 with 2 V peak-to-peak driving voltage in a push–pull configuration for binary transmission of a non-return-to-zero data stream over 50 km of single-mode fibre. This device is the key building block for graphene-based integrated photonics, enabling compact and energy-efficient hybrid graphene–silicon modulators for telecom, datacom and other applications. A 10 Gb s–1 phase modulator based on a graphene-on-silicon Mach–Zehnder interferometer (MZI) is reported. The compact device has a phase-shifter length of only 300 μm and provides modulation of light at 1,550 nm with a 35 dB extinction ratio.

GST-on-silicon hybrid nanophotonic integrated circuits: a non-volatile quasi-continuously reprogrammable platform

Abstract: Reconfiguration of silicon photonic integrated circuits relying on the weak, volatile thermo-optic or electro-optic effect of silicon usually suffers from a large footprint and energy consumption. Here, integrating a phase-change material, Ge2Sb2Te5 (GST) with silicon microring resonators, we demonstrate an energy-efficient, compact, non-volatile, reprogrammable platform. By adjusting the energy and number of free-space laser pulses applied to the GST, we characterize the strong broadband attenuation and optical phase modulation effects of the platform, and perform quasi-continuous tuning enabled by thermo-optically-induced phase changes. As a result, a non-volatile optical switch with a high extinction ratio, as large as 33 dB, is demonstrated.

High-speed silicon modulators for the 2 μm wavelength band

Abstract: The 2 μm wavelength band has become a promising candidate to be the next communication window. We demonstrate high-speed modulators based on a 220 nm silicon-on-insulator platform working at a wavelength of 1950 nm, using the free carrier plasma dispersion effect in silicon. A Mach–Zehnder interferometer modulator and a microring modulator have been characterized. At 1950 nm, the carrier-depletion modulator operates at a data rate of 20 Gbit/s with an extinction ratio of 5.8 dB and insertion loss of 13 dB. The modulation efficiency (V π ·L π ) is 2.68 V·cm at 4 V reverse bias. The device operation is broadband, and we also characterize its performance at 1550 nm. At 1550 nm, an open eye is obtained at 30 Gbit/s. The difference in bandwidth is caused by the bandwidth limit of the 2 μm measurement setup. We also show a ring modulator paired with a low power integrated driver working in hybrid carrier depletion and injection mode at a data rate of 3 Gbit/s with power consumption of 2.38 pJ/bit in the 2 μm wavelength range. This work is a proof of principle demonstration and paves a route toward a full silicon-based transceiver in the 2 μm window.

Gigahertz speed operation of epsilon-near-zero silicon photonic modulators

Abstract: Optical communication systems increasingly require electro-optical modulators that deliver high modulation speeds across a large optical bandwidth with a small device footprint and a CMOS-compatible fabrication process Although silicon photonic modulators based on transparent conducting oxides (TCOs) have shown promise for delivering on these requirements, modulation speeds to date have been limited Here, we describe the design, fabrication, and performance of a fast, compact electroabsorption modulator based on TCOs The modulator works by using bias voltage to increase the carrier density in the conducting oxide, which changes the permittivity and hence optical attenuation by almost 10 dB Under bias, light is tightly confined to the conducting oxide layer through nonresonant epsilon-near-zero (ENZ) effects, which enable modulation over a broad range of wavelengths in the telecommunications band Our approach features simple integration with passive silicon waveguides, the use of stable inorganic materials, and the ability to modulate both transverse electric and magnetic polarizations with the same device design Using a 4-μm-long modulator and a drive voltage of 2 Vpp, we demonstrate digital modulation at rates of 25 Gb/s We report broadband operation with a 65 dB extinction ratio across the 1530–1590 nm band and a 10 dB insertion loss This work verifies that high-speed ENZ devices can be created using conducting oxide materials and paves the way for additional technology development that could have a broad impact on future optical communications systems

Multifunctional meta-mirror: polarization splitting and focusing

Abstract: Metasurfaces are paving the way to improve traditional optical components by integrating multiple functionalities into one optically flat metasurface design. We demonstrate the implementation of a multifunctional gap surface plasmon-based metasurface which, in reflection mode, splits orthogonal linear light polarizations and focuses into different focal spots. The fabricated configuration consists of 50 nm thick gold nanobricks with different lateral dimensions, organized in an array of 240 nm × 240 nm unit cells on the top of a 50 nm thick silicon dioxide layer, which is deposited on an optically thick reflecting gold substrate. Our device features high efficiency (up to ∼65%) and polarization extinction ratio (up to ∼30 dB), exhibiting broadband response in the near-infrared band (750-950 nm wavelength) with the focal length dependent on the wavelength of incident light. The proposed optical component can be forthrightly integrated into photonic circuits or fiber optic devices.

Design Space Exploration of Microring Resonators in Silicon Photonic Interconnects: Impact of the Ring Curvature

Abstract: A detailed analysis of fundamental tradeoffs between ring radius and coupling gap size is presented to draw realistic borders of the possible design space for microring resonators (MRRs). The coupling coefficient for the ring-waveguide structure is estimated based on an integration of the nonuniform gap between the ring and the waveguide. Combined with the supermode analysis of two coupled waveguides, this approach is further expanded into a closed-form equation that describes the coupling strength. This equation permits to evaluate how the distance separating a waveguide from a ring resonator, and the ring radius, affect coupling. The effect of ring radius on the bending loss of the ring is furthermore modeled based on the measurements for silicon MRRs with different radii. These compact models for coupling and loss are subsequently used to derive the main optical properties of MRRs, such as 3-dB optical bandwidth, extinction ratio of resonance, and insertion loss, hence identifying the design space. Our results indicate that the design space for add-drop filters in a wavelength division multiplexed link is currently limited to 5–10 $\mu$ m in radius and gap sizes ranging from 120 to 210 nm. The good agreement between the results from the proposed compact model for coupling and the numerical FDTD and experimental measurements indicate the application of our approach in realizing fast and efficient design space exploration of MRRs in silicon photonic interconnects.

Design of a High Extinction Ratio Tunable Graphene on White Graphene Polarizer

Abstract: A thermally/electrically tunable graphene on white graphene polarizer is proposed, in which the resonant coupling between the plasmonic surface modes of the structure and the transverse electric (TE) [or transverse magnetic (TM)] polarized incident wave is used to absorb this polarization, while the TM (or TE) polarized incident wave is totally reflected. It is then shown that the thermal and electrical tunability of surface conductivity of graphene can be used to control the optical properties of the proposed polarizer, including the selection of the desired polarization, and adjusting the amplitude of the reflected (desired) polarization. The application of the hexagonal boron-nitride (white graphene) as the substrate of graphene increases the propagation of the surface waves of the structure, which in turn results in the very high polarization extinction ratio of 75 dB. Moreover, the ultra-small insertion loss of 0.022 dB and relatively large bandwidth of ~ 60 nm are calculated for the proposed polarizer.

A highly polarization sensitive antimonene photodetector with a broadband photoresponse and strong anisotropy

Abstract: Photodetectors based on two-dimensional materials have shown impressive performance including fast and broadband photoresponse and high responsivity However, their polarization sensitivity remains to be improved Here, we propose an antimonene photodetector having a strong polarization sensitivity with a broadband photoresponse, based on quantum transport calculations A robust photocurrent is generated for almost the whole visible range under small bias, and it saturates at a small bias voltage for most of the photon energies The photocurrent shows a perfect cosine dependence on the polarization angle, which originates from a second-order response to the electric field of the light This leads to a strong polarization sensitivity to the linearly polarized light with a large extinction ratio For a higher photon energy around 32 eV, a rather high extinction ratio greater than 100 can be achieved along with a larger photocurrent Moreover, there is an evident anisotropy between the armchair and zigzag directions, as the photocurrent intensity in the zigzag direction can be approximately 17 times larger than that in the armchair direction at a small bias These results suggest that antimonene is a promising candidate for anisotropic photodetection in the visible range especially for high frequency visible light

Lithium Niobate Electro-Optic Racetrack Modulator Etched in Y-Cut LNOI Platform

Abstract: An electro-optic modulator (EOM) based on a racetrack resonator coupled to a waveguide using butterfly multi-mode interference (MMI) coupler is fabricated on Y-cut lithium niobate (LN) thin film This is the first demonstration of a LN EOM in which the thin film of LN is etched in a Y-cut substrate using chlorine-based inductively coupled plasma reactive ion etching, a process, which is readily compatible with semiconductor fabrication facility The Y-cut LNOI platform is interesting for the integration of electro-optic and acousto-optic components, since differently from any other LN cut it facilitates taking advantage of the maximum electro-optic and piezoelectric coefficients of LN Coupling to the racetrack was enabled using a butterfly MMI coupler, which offered operation near the critical coupling condition, hence increasing the extinction ratio (ER) of the modulator An unloaded quality factor of 13 × 105 was extracted for this device, which is equivalent to a propagation loss of 23 dB/cm Modulation bandwidth of 4 GHz, wavelength tuning rate of 032 pm/V, and an ER of more than 10 dB were experimentally measured for the EOM

Rochon-Prism-Like Planar Circularly Polarized Beam Splitters Based on Dielectric Metasurfaces

Abstract: We design and fabricate the Rochon-prism-like planar circularly polarized beam splitters based on dielectric metasurfaces by simultaneously controlling the geometric phase and the propagation phase via manipulation of the orientations and the sizes of the constituent silicon nanoblocks. The special splitters deviate only one of the circular polarizations while leave the other undeviated, acting like a Rochon prism for linearly polarized light, and their efficiencies can be as high as 66.7% with an extinction ratio of 27. The mechanism makes it possible to fabricate metasurface holograms that can only be reconstructed by either of two circular polarizations while hidden from the other. The functionality of beam splitting and polarization dependent decryption based on dielectric metasurfaces enables the potential applications in both miniaturized polarizing optical systems and information security and processing.

Silicon Photonic Switch Subsystem With 900 Monolithically Integrated Calibration Photodiodes and 64-Fiber Package

Abstract: A packaged and fully operational 32 × 32 silicon photonic switch chip having 448 switch cells and 1856 crossings is demonstrated. The switch chip includes 900 monolithically integrated photodiodes used for calibrating the thermo-optic Mach–Zehnder switch cells. The calibration procedure employs an external laser source and follows a reachability-tree sequence to calibrate all switch cells. The accuracy of the calibration is demonstrated by the measurement of switch cell extinction ratios, for both states of each switch cell. The mean extinction ratio for both states is 35 dB. Arbitrary light path switching is demonstrated. Measurement of the channel-to-channel crosstalk was performed for a large number of aggressor and victim light path combinations. The matrix crosstalk is dominated by contributions from waveguide crossings. The die was wire-bonded to a custom ceramic package, to which a 68-fiber ribbon was permanently attached, which coupled the input and output optical signals to edge couplers on the chip through a waveguide pitch- and mode-concentrating silica chip. The fiber-to-fiber loss of on-chip loopback waveguides was less than 6.5 dB from 1530 to 1565 nm. The entirety of switch cells and monitors was driven by controller boards and A/D chips using a controller field-programmable gate array (FPGA). The calibration procedure was completed in less than 10 min using only the on-chip monitors, without off-chip detectors. The chip was recalibrated after six months storage, and the measured change in drive current was within the calibration uncertainty, indicating that the chip and driver are stable over time.

3.2-MP Back-Illuminated Polarization Image Sensor With Four-Directional Air-Gap Wire Grid and 2.5- $\mu$ m Pixels

Abstract: A 3.2-MP four-directional polarization image sensor with air-gap wire-grid polarizer is described. The image sensor was fabricated using a wafer process and incorporates back-illumination and an antireflection layer to minimize optical flaring and ghosting problems. In testing, the sensor achieved a polarization transmittance of 63.3% and an extinction ratio of 85 at 550 nm, thereby outperforming conventional polarization sensors. The proposed sensor also exhibited good oblique-incidence characteristics, even with small polarization pixels of $2.5~\mu \text{m}$ . Based on these results, the proposed image sensor is suitable for various megapixel fusion-imaging applications, such as reducing surface reflections, highly accurate depth mapping, and condition-robust surveillance.

Single-polarization single-mode double-ring hollow-core anti-resonant fiber.

Abstract: A novel single-polarization single-mode double-ring hollow-core anti-resonant fiber with two single-polarization regions (1545–1553 nm and 1591–1596 nm) is proposed. Single-polarization guidance is achieved by coupling a polarized fundamental mode and silica mode by using different tube thicknesses. Specifically, when the wavelength is 1550 nm, only a single x-polarized fundamental mode with a low loss of 0.04 dB/m is propagated by a polarization extinction ratio of 17662 and minimum higher-order mode extinction ratio of 393 by optimizing the structural parameters. Furthermore, this fiber also exhibits high-performance bend resistance. The x-polarized FM loss is as low as 0.11 dB/m with single-polarization single-mode guidance when the proposed fiber was bent at a bend radius of 8 cm toward the x-direction.

Polarization-insensitive 2 × 2 thermo-optic Mach-Zehnder switch on silicon.

Abstract: A polarization-insensitive 2×2 thermo-optic Mach–Zehnder switch (MZS) on silicon is proposed and demonstrated experimentally by utilizing silicon-on-insulator (SOI) nanophotonic waveguides with a 340-nm-thick silicon core layer. The present MZS consists of two 2×2 3 dB multimode interference (MMI) couplers, which are designed to be polarization-insensitive by choosing the core width optimally. Meanwhile, the MZS arms are designed with square SOI nanophotonic waveguides with a cross section of 340 nm×340 nm in order to achieve polarization-insensitive phase shift. The fabricated silicon MZS has an excess loss of 1∼4 dB and an extinction ratio of >20 dB in the C-band (1530∼1565 nm) for both TM and TE polarizations.

High-extinction-ratio directional-coupler-type polarization beam splitter with a bridged silicon wire waveguide

Abstract: We demonstrate an integrated polarization beam splitter (PBS) of a simple and compact device geometry with high polarization extinction ratios (PERs). A silicon PBS based on a three-waveguide directional coupler is numerically simulated for optimum device parameters, and fabricated experimentally. The measured PER values of the fabricated PBSs are 40.74 dB and 39.01 dB for transverse electric and transverse magnetic modes, respectively, and their corresponding insertion losses are 0.35 dB on average for a coupler length of about 29.4 μm.

Experimental demonstration of dissipative sensing in a self-interference microring resonator

Abstract: The dissipative sensing based on a self-interference microring resonator composed of a microring resonator and a U-shaped feedback waveguide is demonstrated experimentally. Instead of a frequency shift induced by the phase shift of the waveguide or the microcavity, the dissipative sensing converts the phase shift to the effective external coupling rate, which leads to the change of linewidth of the optical resonance and the extinction ratio in the transmission spectrum. In our experiment, the power dissipated from a microheater on the feedback waveguide is detected by the dissipative sensing mechanism, and the sensitivity of our device can achieve 0.22 dB/mW. This dissipative sensing mechanism provides another promising candidate for microcavity sensing applications.

Significantly High Modulation Efficiency of Compact Graphene Modulator Based on Silicon Waveguide.

Abstract: We theoretically and experimentally demonstrate a significantly large modulation efficiency of a compact graphene modulator based on a silicon waveguide using the electro refractive effect of graphene. The modulation modes of electro-absorption and electro-refractive can be switched with different applied voltages. A high extinction ratio of 25 dB is achieved in the electro-absorption modulation mode with a driving voltage range of 0 V to 1 V. For electro-refractive modulation, the driving voltage ranges from 1 V to 3 V with a 185-pm spectrum shift. The modulation efficiency of 1.29 V · mm with a 40-μm interaction length is two orders of magnitude higher than that of the first reported graphene phase modulator. The realisation of phase and intensity modulation with graphene based on a silicon waveguide heralds its potential application in optical communication and optical interconnection systems.

Graphene oxide and reduced graphene oxide as saturable absorbers onto D-shaped fibers for sub 200-fs EDFL mode-locking

Abstract: We present high mode-locking performances from an erbium-doped fiber laser (EDFL) by using graphene oxide (GO) and reduced graphene oxide (r-GO) as saturable absorbers (SA) deposited onto the polished surface of a D-shaped optical fiber. The samples were prepared with different concentrations and its characterization was performed by using an optical microscope, a Raman spectrometer, nonlinear saturable absorption measurements, polarization setup, and laser mode-locking analysis. As a 1550-nm polarizer, the best GO (r-GO) samples exhibited higher polarization extinction ratio (PER) of 7.94 (7.65) dB, corresponding to 84 (83) %, both showing similar graphene TE absorption behavior. In a managed-intracavity dispersion laser, broadest bandwidths of 27.2 and 24.1 nm and the corresponding shortest pulse duration of 190 fs could be generated when incorporating the SA with high modulation depth (above 20%), being so far the best mode-locking results ever reported in the literature for GO and r-GO SA onto D-shaped optical fibers in EDFL.

A Photonic Switch Based on a Hybrid Combination of Metallic Nanoholes and Phase-change Vanadium Dioxide.

Abstract: A photonic switch is an integral part of optical telecommunication systems. A plasmonic bandpass filter integrated with materials exhibiting phase transition can be used as a thermally reconfigurable optical switch. This paper presents the design and demonstration of a broadband photonic switch based on an aluminium nanohole array on quartz utilising the semiconductor-to-metal phase transition of vanadium dioxide. The fabricated switch shows an operating range over 650 nm around the optical communication C, L, and U band with maximum 20%, 23% and 26% transmission difference in switching in the C band, L band, and U band, respectively. The extinction ratio is around 5 dB in the entire operation range. This architecture is a precursor for developing micron-size photonic switches and ultra-compact modulators for thin film photonics.

Ultra-large core birefringent Yb-doped tapered double clad fiber for high power amplifiers

Abstract: We present a birefringent Yb-doped tapered double-clad fiber with a record core diameter of 96 µm. An impressive gain of over 38 dB was demonstrated for linearly polarized CW and pulsed sources at a wavelength of 1040 nm. For the CW regime the output power was70 W. For a mode-locked fiber laser a pulse energy of 28 µJ with 292 kW peak power was reached at an average output power of 28 W for a 1 MHz repetition rate. The tapered double-clad fiber has a high value of polarization extinction ratio at 30 dB and is capable of delivering the linearly polarized diffraction-limited beam (M2 = 1.09).

Simultaneous strain and temperature sensor based on polarization maintaining fiber and multimode fiber

Abstract: A novel, simultaneous strain and temperature sensor utilizing polarization maintaining fiber (PMF) and multimode fiber (MMF) is proposed and experimentally demonstrated in this paper. The sensing head of this sensor can be obtained by splicing PMF and MMF in the structure of PMF-MMF-PMF. The extinction ratio of the transmission spectrum can be over 30 dB. The strain sensitivities of sensor by two spectrum dips can be 1.01 pm/μe and 1.27 pm/μe in the range from 0 to 2000 μe. Meanwhile, the temperature sensitivities of 49 pm/°C and 41 pm/°C can be achieved by two spectrum dips in the range from 30 °C to 70 °C. The sensitivity difference between the two spectrum dips can be used to realize dual parameters fiber sensing. This sensor exhibits the advantages of simple fabrication, compact structure and multi-purpose measuring. It may have the great potential in fields of robot arms and artificial limbs.

$2-\mu$ m Wavelength Grating Coupler, Bent Waveguide, and Tunable Microring on Silicon Photonic MPW

Abstract: The $2-\mu \text{m}$ wave band is emerging as a promising spectral window for optical communications and gas sensing. With the increasing demand for components at this wavelength range, developing $2-\mu \text{m}$ devices is thus required. Silicon photonics is an ideal device technology as it offers several unique advantages of potential low cost and large scale integration. Besides, the silicon nanowire waveguide is transparent and suffers from negligible two photon absorption at $2-\mu \text{m}$ wavelengths. Here, we report the demonstration of grating coupler, waveguide bend, and thermally tunable microring filter on a multi-project wafer which is fabricated using CMOS compatible process. The peak coupling efficiency of the grating coupler is measured to be −8.4 dB at 1952 nm. The bending losses for the rib waveguide and the strip loaded waveguide are measured with different radii. The ring resonator is fabricated and tested with an underestimated $Q$ factor of 1520 (through port) which is due to the limitation of the laser linewidth and wavelength tuning resolution. The extinction ratio exceeds 20 dB and the ring resonance can be thermally tuned by a Titanium Nitride heater. The tuning efficiency is 0.17 nm/mW.

Atomic Scale Photodetection Enabled by a Memristive Junction

Abstract: The optical control of atomic relocations in a metallic quantum point contact is of great interest because it addresses the fundamental limit of “CMOS scaling”. Here, by developing a platform for combined electronics and photonics on the atomic scale, we demonstrate an optically controlled electronic switch based on the relocation of atoms. It is shown through experiments and simulations how the interplay between electrical, optical, and light-induced thermal forces can reversibly relocate a few atoms and enable atomic photodetection with a digital electronic response, a high resistance extinction ratio (70 dB), and a low OFF-state current (10 pA) at room temperature. Additionally, the device introduced here displays an optically induced pinched hysteretic current (optical memristor). The photodetector has been tested in an experiment with real optical data at 0.5 Gbit/s, from which an eye diagram visualizing millions of detection cycles could be produced. This demonstrates the durability of the realized ...

High-contrast and low-power all-optical switch using Fano resonance based on a silicon nanobeam cavity

Abstract: We experimentally demonstrate an ultra-compact all-optical switch involving Fano resonance based on a side-coupled Fabry–Perot (F-P) resonator and a silicon photonic crystal (PhC) nanobeam cavity, with an area of only 11 μm2. By optimizing the structure of the nanobeam cavity to increase its intrinsic quality factor (Q), we achieve a sharp asymmetric transmission spectrum, with an extinction ratio (ER) as high as 40 dB and a peak loss as low as 0.6 dB. As far as we know, this is the highest measured ER in PhC-based Fano resonance. These excellent properties enable us to realize an all-optical switch with shorter switching recovery time, lower power consumption, and higher contrast, compared to that involving Lorentzian resonance. For example, under signal trains of 2.5 Gb/s, switching energy with a contrast of 3 dB for the Fano case is 113 fJ, which is 8 dB smaller than that for the Lorentzian case. Furthermore, by performing blue-detuned filtering on the 15-Gb/s output signal light, the switching contrast of the all-optical switch based on Fano resonance is significantly improved from 0.67 dB to 9.53 dB.

CMOS compatible all-silicon TM pass polarizer based on highly doped silicon waveguide

Abstract: We propose and analyze via simulation a novel approach to implement a complementary metal-oxide-semiconductor compatible and high extinction ratio transverse magnetic pass polarizer on the silicon-on-insulator platform with a 340 nm thick silicon core. The TM-pass polarizer utilizes a highly doped p-silicon waveguide as the transverse hybrid plasmonic waveguide. We observed an extinction ratio of 30.11 dB and an insertion loss of 3.08 dB for a device length of 15 µm. The fabrication process of the proposed TM-pass polarizer is simpler compared to the state-of-the-art since it only uses silicon waveguides and does not require any special material or feature size.

Ultrashort and broadband silicon polarization splitter-rotator using fast quasiadiabatic dynamics.

Abstract: We propose an ultrashort and broadband silicon mode-conversion polarization splitter-rotator (PSR) consisting of a taper and a Y-junction both designed by the fast quasiadiabatic dynamics (FAQUAD). The FAQUAD is used to homogeneously distribute adiabaticity over the length of the PSR, providing shortcut to adiabaticity at a shorter device length. The total length of the silicon PSR is 39.2 μm. For a wavelength range from 1.5 μm to 1.6 μm, the PSR exhibits a good performance with > 88% transmission and > 11.4 dB extinction ratio (ER). Simulations also show that the designed devices have good fabrication tolerance.

One-volt silicon photonic crystal nanocavity modulator with indium oxide gate.

Abstract: The ever-increasing global network traffic requires a high level of seamless integration between optical interconnect systems and complementary metal–oxide–semiconductor (CMOS) circuits. Therefore, it brings stringent requirements for future electro-optic (E-O) modulators, which should be ultracompact, energy efficient, high bandwidth, and in the meanwhile, able to be directly driven by the state-of-the-art CMOS circuits. In this Letter, we report a low-voltage silicon photonic crystal nanocavity modulator using an optimized metal–oxide–semiconductor (MOS) capacitor consisting of an In2O3/HfO2/p-Si stacked nanostructure. The strong light–matter interaction from the accumulated free carriers with the nanocavity resonant mode results in holistic improvement in device performance, including a high tuning efficiency of 250 pm/V and an average modulation strength of 4 dB/V with a moderate Q factor of ∼3700 and insertion loss of ∼6 dB using an ultrashort electrode length of only 350 nm. With 1 V driving voltage over a capacitive loading of only 13 fF, the silicon photonic nanocavity modulator can achieve more than 3 dB extinction ratio with energy consumption of only 3 fJ/bit. Such a low-voltage, low-capacitance silicon nanocavity modulator provides the feasibility to be directly driven by a CMOS logic gate for single-chip integration.

Compact silicon TE-pass polarizer using adiabatically-bent fully-etched waveguides.

Abstract: A high-performance integrated silicon TE-pass polarizer is proposed and demonstrated. The polarizer uses a series of adiabatic waveguide bends that yield high extinction ratio for the TM polarization and low insertion loss for the TE polarization, and does not require special materials or complex fabrication steps. The polarizer, implemented on a silicon-on-insulator platform with a 220 nm silicon thickness, is measured to have insertion loss ≤ 0.37 dB (average 0.12 dB) and extinction ratio ≥ 27.6 dB (average 36.0 dB) over a 1.5 μm to 1.6 μm wavelength range, with a footprint of 63 μm × 9.5 μm. The trade-off between the footprint of the polarizer and its performance is established. While the analysis was done for a silicon-on-insulator platform, the concept is applicable to other waveguide geometries and integrated photonic platforms.

Silicon-Based Hybrid (de)Multiplexer for Wavelength-/Polarization-Division-Multiplexing

Abstract: A novel hybrid multiplexer for wavelength-division- multiplexing (WDM) and polarization-division-multiplexing (PDM) is proposed and realized by integrating a polarization-splitter-rotator (PSR) and an optical-filter array based on novel microring resonators (MRRs). With the PSR, the launched TM-polarized light is rotated to be TE-polarized and outputs from the cross port while the launched TE-polarized light outputs from the through port directly. In the proposed novel configuration, the cross- and through-ports of the PSR are connected through the bus waveguide for all the MRR-based optical filters. In this way, each MRR-based optical filter works bidirectionally and has two drop ports, from which the same wavelength channel of TE- and TM-polarizations are dropped separately. As an example, a 16-channel hybrid WDM-PDM multiplexer is designed and realized with eight wavelength channels and dual polarizations by integrating a PSR and eight MRR-based optical filters with box-like responses. The fabricated PSR has an excess loss of ∼0.6 dB and an extinction ratio (ER) of ∼20 dB in the wavelength range from 1550 to 1580 nm. The optical filters are designed by using cascaded MRRs with bent directional couplers, which works for TE polarization only with very high ER (>35 dB) and, thus, reduces the polarization crosstalk greatly. For the MRR-based optical filters of the present hybrid (de)multiplexer, the channel spacing is 400 GHz (3.2 nm), the crosstalk between the adjacent channels is μ m × 300 μ m. The present hybrid (de)multiplexer can be extended for more channels by reducing the channel spacing as well as increasing the free-spectral range of the MRRs.