InGaAs/GaAs nano-ridge laser with an amorphous silicon grating monolithically grown on a 300†mm Si wafer.

The monolithic growth of direct-bandgap III-V materials directly on a Si substrate is a promising approach for the fabrication of complex silicon photonic integrated circuits including light sources and amplifiers. It remains challenging to realize practical, reliable, and efficient light emitters due to misfit defect formation during the epitaxial growth. Exploiting nano-ridge engineering (NRE), III-V nano-ridges with high crystal quality were achieved based on aspect ratio defect trapping inside narrow trenches. In an earlier work, we used an etched grating to create distributed feedback lasers from these nano-ridges. Here we deposited an amorphous silicon grating on the top of the nano-ridge. Under pulsed optical pumping, a ∼7.84 kW/cm2 lasing threshold was observed, ∼5 times smaller compared to devices with an etched grating inside the nano-ridge. Compared to the etched grating, the amorphous silicon grating introduces no extra carrier loss channels through surface state defects, which is believed to be the origin of the lower threshold. This low threshold again demonstrates the high quality of the epitaxial deposited material and may provide a route toward further optimizing the electrically driven devices.

Lanthanide-Assisted Deposition of Strongly Electro-optic PZT Thin Films on Silicon: Toward Integrated Active Nanophotonic Devices.

The electro-optical properties of lead zirconate titanate (PZT) thin films depend strongly on the quality and crystallographic orientation of the thin films. We demonstrate a novel method to grow highly textured PZT thin films on silicon using the chemical solution deposition (CSD) process. We report the use of ultrathin (5-15 nm) lanthanide (La, Pr, Nd, Sm) based intermediate layers for obtaining preferentially (100) oriented PZT thin films. X-ray diffraction measurements indicate preferentially oriented intermediate Ln2O2CO3 layers providing an excellent lattice match with the PZT thin films grown on top. The XRD and scanning electron microscopy measurements reveal that the annealed layers are dense, uniform, crack-free and highly oriented (>99.8%) without apparent defects or secondary phases. The EDX and HRTEM characterization confirm that the template layers act as an efficient diffusion barrier and form a sharp interface between the substrate and the PZT. The electrical measurements indicate a dielectric constant of ∼650, low dielectric loss of ∼0.02, coercive field of 70 kV/cm, remnant polarization of 25 µC/cm(2), and large breakdown electric field of 1000 kV/cm. Finally, the effective electro-optic coefficients of the films are estimated with a spectroscopic ellipsometer measurement, considering the electric field induced variations in the phase reflectance ratio. The electro-optic measurements reveal excellent linear effective pockels coefficients of 110 to 240 pm/V, which makes the CSD deposited PZT thin film an ideal candidate for Si-based active integrated nanophotonic devices.

Plasmonic-organic hybrid (POH) modulators for OOK and BPSK signaling at 40 Gbit/s.

We report on high-speed plasmonic-organic hybrid Mach-Zehnder modulators comprising ultra-compact phase shifters with lengths as small as 19 µm. Choosing an optimum phase shifter length of 29 µm, we demonstrate 40 Gbit/s on-off keying (OOK) modulation with direct detection and a BER < 6 × 10(-4). Furthermore, we report on a 29 µm long binary-phase shift keying (BPSK) modulator and show that it operates error-free (BER < 1 × 10(-10)) at data rates up to 40 Gbit/s and with an energy consumption of 70 fJ/bit.

Heterogeneously integrated III-V/silicon distributed feedback lasers.

Heterogeneously integrated III-V-on-silicon second-order distributed feedback lasers utilizing an ultra-thin DVS-BCB die-to-wafer bonding process are reported. A novel DFB laser design exploiting high confinement in the active waveguide is demonstrated. A 14 mW single-facet output power coupled to a silicon waveguide, 50 dB side-mode suppression ratio and continuous wave operation up to 60°C around 1550 nm is obtained.

Unidirectional III-V microdisk lasers heterogeneously integrated on SOI.

We demonstrate unidirectional bistability in microdisk lasers electrically pumped and heterogeneously integrated on SOI. The lasers operate in continuous wave regime at room temperature and are single mode. Integrating a passive distributed Bragg reflector (DBR) on the waveguide to which the microdisk is coupled feeds laser emission back into the laser cavity. This introduces an extra unidirectional gain and results in unidirectional emission of the laser, as demonstrated in simulations as well as in experiment.

III-V-on-silicon multi-frequency lasers.

Compact multi-frequency lasers are realized by combining III-V based optical amplifiers with silicon waveguide optical demultiplexers using a heterogeneous integration process based on adhesive wafer bonding. Both devices using arrayed waveguide grating routers as well as devices using ring resonators as the demultiplexer showed lasing with threshold currents between 30 and 40 mA and output powers in the order of a few mW. Laser operation up to 60°C is demonstrated. The small bending radius allowable for the silicon waveguides results in a short cavity length, ensuring stable lasing in a single longitudinal mode, even with relaxed values for the intra-cavity filter bandwidths.

Uniformity of the lasing wavelength of heterogeneously integrated InP microdisk lasers on SOI.

We report a high lasing wavelength uniformity of optically pumped InP-based microdisk lasers processed with electron-beam lithography, heterogeneously integrated with adhesive bonding on silicon-on-insulator (SOI) waveguide circuits and evanescently coupled to an underlying waveguide. We study the continuous wave laser emission coupling out of the SOI via a grating coupler etched at one side of the waveguide, and demonstrate a standard deviation in lasing wavelength of nominally identical devices on the same chip lower than 500 pm. The deviation in the diameter of the microdisks as low as a few nanometers makes all-optical signal processing applications requiring cascadability possible.

Compact SOI-based polarization diversity wavelength de-multiplexer circuit using two symmetric AWGs.

We demonstrate a compact 16-channel 200 GHz polarization diversity wavelength de-multiplexer circuit using two silicon AWGs and 2D grating couplers. Estimated fiber to fiber loss is better than -15.0 dB. Insertion loss and crosstalk induced by the AWGs are -2.6 dB and 21.5 dB, respectively. The maximum polarization dependent wavelength shift is 0.12 nm. The polarization dependent loss varies between 0.06 dB and 2.32 dB over the 16 channels. The total circuit footprint is 1400 × 850 µm(2).

Ultracompact electro-optic phase modulator based on III-V-on-silicon microdisk resonator.

A novel ultracompact electro-optic phase modulator based on a single 9 µm-diameter III-V microdisk resonator heterogeneously integrated on and coupled to a nanophotonic waveguide is presented. Modulation is enabled by effective index modification through carrier injection. Proof-of-concept implementation involving binary phase shift keying modulation format is assembled. A power imbalance of ∼0.6 dB between both symbols and a modulation rate up to 1.8 Gbps are demonstrated without using any special driving technique.

Parametric instability of an integrated micromechanical oscillator by means of active optomechanical feedback.

Mass sensing and time keeping applications require high frequency integrated micromechanical oscillators. To overcome the increasing mechanical stiffness of these structures sensitive optical vibration detection and efficient actuation is required. Therefore we have implemented an active feedback system, where the feedback signal is provided by the optical gradient force that is present between nanophotonic waveguides on a silicon-on-insulator chip. We found that access to the parametric instability regime can be easily controlled by tuning the wavelength.

Bias-free, low power and optically driven membrane InP switch on SOI for remotely configurable photonic packet switches.

A small footprint integrated Membrane InP Switch (MIPS) on Silicon-On-Insulator (SOI) is demonstrated for use in all-optical packet switching. The device consists of an optically pumped III-V membrane waveguide of only 100 nm thick, coupled to the underlying SOI waveguide circuit. Because of its limited thickness, the optical confinement in the active layers is maximized, allowing for high extinction ratio of over 30 dB when applying a low power optical pump signal, over the entire C-band. The switch has 400/1300 ps on/off switching times and no measurable pattern dependence or switching related power penalties for a bitrate up to 40 Gb/s, using a switching power of only 2 dBm.

Generation of correlated photons in hydrogenated amorphous-silicon waveguides.

We report the first (to our knowledge) observation of correlated photon emission in hydrogenated amorphous-silicon waveguides. We compare this to photon generation in crystalline silicon waveguides with the same geometry. In particular, we show that amorphous silicon has a higher nonlinearity and competes with crystalline silicon in spite of higher loss.

High-efficiency fiber-to-chip grating couplers realized using an advanced CMOS-compatible silicon-on-insulator platform.

A new generation of Silicon-on-Insulator fiber-to-chip grating couplers which use a silicon overlay to enhance the directionality and thereby the coupling efficiency is presented. Devices are realized on a 200 mm wafer in a CMOS pilot line. The fabricated fiber couplers show a coupling efficiency of -1.6 dB and a 3 dB bandwidth of 80 nm.

Bridging the gap between nanophotonic waveguide circuits and single mode optical fibers using diffractive grating structures.

In this paper, the use of diffractive grating structures to efficiently interface between a single mode fiber and a high index contrast waveguide circuit is outlined. We show that high index contrast grating structures allow for broadband and high efficiency coupling. Since no polished facet is required on the photonic integrated circuit to interface with the optical fiber, fiber-to-chip grating couplers enable wafer-scale testing, reducing the cost for testing large scale integrated optical circuits. We show that two-dimensional grating structures can solve the problem of the huge polarization dependence of high index contrast photonic integrated circuits. Finally, an optical probe is presented, which allows testing individual components of a photonic integrated circuit, analogous to the electrical probes used in micro-electronics.

Trimming of silicon ring resonator by electron beam induced compaction and strain.

Silicon is becoming the preferable platform for future integrated components, mostly due to the mature and reliable fabrication capabilities of electronics industry. Nevertheless, even the most advanced fabrication technologies suffer from non-uniformity on wafer scale and on chip scale, causing variations in the critical dimensions of fabricated components. This is an important issue since photonic circuits, and especially cavities such as ring resonators, are extremely sensitive to these variations. In this paper we present a way to circumvent these problems by trimming using electron beam induced compaction of oxide in silicon on insulator. Volume compaction of the oxide cladding causes both changes in the refractive index and creates strain in the silicon lattice. We demonstrate a resonance wavelength red shift 4.91 nm in a silicon ring resonator.

Electrophoretic deposition of ZnO nanoparticles, from micropatterns to substrate coverage.

We report on an electrophoretic deposition (EPD) method that is suited for the preparation of both ZnO thin films and micropatterns. By applying small DC voltages between a Cu electrode and a conductive Si substrate, submersed in a suspension of ZnO quantum dots, we can cover entire substrates with ZnO layers of a tuneable thickness ranging from a few monolayers to 200 nm. The deposition occurs selectively at the cathode, which indicates that the ZnO particles have a positive charge. Atomic force microscopy was used to study the influence of the deposition voltage, time, and the quantum dot concentration on the final layer thickness. By using lithographically patterned Si substrates, the same technique enables the formation of ZnO micropatterns of variable thickness with dimensions down to 5 µm. This is done by depositing a ZnO layer on a Si substrate that is covered with a patterned, developed photoresist. After EPD, the resist is removed by submersing the substrate in the appropriate solvent without damaging the ZnO deposit. This illustrates the robustness of the layers obtained by EPD.

Electrically pumped InP-based microdisk lasers integrated with a nanophotonic silicon-on-insulator waveguide circuit.

A compact, electrically driven light source integrated on silicon is a key component for large-scale integration of electronic and photonic integrated circuits. Here we demonstrate electrically injected continuous-wave lasing in InP-based microdisk lasers coupled to a sub-micron silicon wire waveguide, fabricated through heterogeneous integration of InP on silicon-on-insulator (SOI). The InP-based microdisk has a diameter of 7.5 mum and a thickness of 1 mum. A tunnel junction was incorporated to efficiently contact the p-side of the pn-junction. The laser emits at 1.6 mum, with a threshold current as low as 0.5 mA under continuous-wave operation at room temperature, and a threshold voltage of 1.65 V. The SOI-coupled laser slope efficiency was estimated to be 30 muW/mA, with a maximum unidirectional output power of 10 muW.

Compact wavelength router based on a Silicon-on-insulator arrayed waveguide grating pigtailed to a fiber array.

We demonstrate a compact, fiber-pigtailed, 4-by-4 wavelength router in Silicon-on-insulator photonic wires, fabricated using CMOS processing methods. The core is an AWG with a 250GHz channel spacing and 1THz free spectral range, on a 425x155 microm(2) footprint. The insertion loss of the AWG was reduced to 3.5dB by applying a two-step processing technique. The crosstalk is -12dB. The device was pigtailed using vertical fiber couplers and an eight-fiber array connector.

Heterogeneous integration of electrically driven microdisk based laser sources for optical interconnects and photonic ICs.

A new approach for an electrically driven microlaser based on a microdisk transferred onto Silicon is proposed. The structure is based on a quaternary InGaAsP p-i-n junction including three InAsP quantum wells, on a thin membrane transferred onto silicon by molecular bonding. A p++/n++ tunnel junction is used as the p-type contact. The technological procedure is described and first experimental results show a laser emission in pulsed regime at room temperature, with a threshold current near 1.5 mA.

Laser emission and photodetection in an InP/InGaAsP layer integrated on and coupled to a Silicon-on-Insulator waveguide circuit.

Laser emission from an InP/InGaAsP thin film epitaxial layer bonded to a Silicon-on-Insulator waveguide circuit was observed. Adhesive bonding using divinyl-tetramethyldisiloxane-benzocyclobutene (DVS-BCB) was used to integrate the InP/InGaAsP epitaxial layers onto the waveguide circuit. Light is coupled from the laser diode into an underlying waveguide using an adiabatic inverted taper approach. 0.9mW optical power was coupled into the SOI waveguide using a 500mum long laser. Besides for use as a laser diode, the same type of devices can be used as a photodetector. 50mum long devices obtained a responsivity of 0.23A/W.