25 × 50 Gbps wavelength division multiplexing silicon photonics receiver chip based on a silicon nanowire-arrayed waveguide grating

Theoretical and experimental investigations of the nonlinear refractive index in an erbium- doped fiber are reported. We also show that an optical switch based on twin-core erbium- doped fiber can be constructed and operated at low input optical power, in the order of 1 or 2 mW. The transient response of this fiber also is examined. The switching speed can be improved by using a signal power at a wavelength close to the resonant wavelength between the excited state and the ground state.

Lithium niobate (LN) is commonly used as an electro optic (EO) Q-switch material in infrared targeting lasers because of its relatively low voltage requirements and low cost compared to other crystals. A common challenge is maintaining good performance at the sub-freezing temperatures often experienced during flight. Dropping to low temperature causes a pyro-electric charge buildup on the optical faces that leads to birefringence non-uniformity and depolarization resulting in poor hold-off and premature lasing. The most common solution has been to use radioactive americium to ionize the air around the crystal and bleed off the charge, but the radioactive material requires handling and disposal procedures that can be problematic. We have developed a superior solution that is now being implemented by multiple defense system suppliers. By applying a low level thermo-chemical reduction to the LN crystal optical faces we induce a small conductivity that allows pyro-charges to dissipate. As the material gets more heavily treated, the capacity to dissipate charges improves, but the corresponding optical absorption also increases, causing insertion loss. Even though typical high gain targeting laser systems can tolerate a few percent of added loss, the thermo-chemical processing needs to be carefully optimized. We describe the results of our process optimization to minimize the insertion loss while still giving effective charge dissipation. Treatment is performed at temperatures below 500°C and a conductivity layer less than 0.5mm in depth is created that is uniform across the optical aperture. Because the conductivity is thermally activated, the charge dissipation is less effective at low temperature, and characterization needs to be performed at cold temperatures. The trade-off between optical insertion loss and potential depolarization due to low temperature operation is discussed and experimental results on the temperature dependence of the dissipation time and the optical loss are reported.

The tremendous demand for low-cost, low-consumption and high-capacity optical transmitters in data centers challenges the current InP-photonics platform. The use of silicon (Si) photonics platform to fabricate photonic integrated circuits (PICs) is a promising approach for low-cost large-scale fabrication considering the CMOS-technology maturity and scalability. However, Si itself cannot provide an efficient emitting light source due to its indirect bandgap. Therefore, the integration of III-V semiconductors on Si wafers allows us to benefit from the III-V emitting properties combined with benefits offered by the Si photonics platform. Direct epitaxy of InP-based materials on 300 mm Si wafers is the most promising approach to reduce the costs. However, the differences between InP and Si in terms of lattice mismatch, thermal coefficients and polarity inducing defects are challenging issues to overcome. III-V/Si hetero-integration platform by wafer-bonding is the most mature integration scheme. However, no additional epitaxial regrowth steps are implemented after the bonding step. Considering the much larger epitaxial toolkit available in the conventional monolithic InP platform, where several epitaxial steps are often implemented, this represents a significant limitation. In this paper, we review an advanced integration scheme of AlGaInAs-based laser sources on Si wafers by bonding a thin InP seed on which further regrowth steps are implemented. A 3 µm-thick AlGaInAs-based MutiQuantum Wells (MQW) laser structure was grown onto on InP-SiO2/Si (InPoSi) wafer and compared to the same structure grown on InP wafer as a reference. The 400 ppm thermal strain on the structure grown on InPoSi, induced by the difference of coefficient of thermal expansion between InP and Si, was assessed at growth temperature. We also showed that this structure demonstrates laser performance similar to the ones obtained for the same structure grown on InP. Therefore, no material degradation was observed in spite of the thermal strain. Then, we developed the Selective Area Growth (SAG) technique to grow multi-wavelength laser sources from a single growth step on InPoSi. A 155 nm-wide spectral range from 1515 nm to 1670 nm was achieved. Furthermore, an AlGaInAs MQW-based laser source was successfully grown on InP-SOI wafers and efficiently coupled to Si-photonic DBR cavities. Altogether, the regrowth on InP-SOI wafers holds great promises to combine the best from the III-V monolithic platform combined with the possibilities offered by the Si photonics circuitry via efficient light-coupling.

Silicon (Si) photonics is an area that has recently attracted great attention. In order to realize the goal of integrated photonic components on an electronics platform, an electrically pumped laser on a Si substrate is required. The usage of III–V compounds has enabled such devices to be grown directly on the Si electronics platform that underpins contemporary electronics. In this paper, semiconductor III–V lasers monolithically grown on Si are reviewed, with quantum well and quantum dot technology being used to obtain lasers operating at wavelengths of 1.05, 1.30, 1.5 and 2 µm, with threshold currents <1 kA cm−2. In addition, an integrated modulator and laser fabricated by epitaxial regrowth has been demonstrated at 1.05 µm with a modulation depth of 45% at −3 V and 100% at −5 V. 1.3 µm lasers grown on Ge and Ge-on-Si substrates with the low continuous wave room-temperature threshold current densities of 55 and 164 A cm−2, respectively are reviewed as a promising approach to obtaining high performance lasers on Si substrates. These results demonstrate that the direct, monolithic growth of III–V compounds on a Si platform is a strong contender for the realization of an optical source integrated on an electronics platform.

We investigate the influence of Zinc diffusion on the modulation efficiency and optical insertion loss of InP-based MZI modulators. By analyzing the electric-optical field distribution and free-carrier absorption loss of three types of Zinc diffusion profiles, the mechanisms between Zn diffusion and modulation efficiency and optical insertion loss inside MZI modulators are systematically studied. We show that InP-based MZI modulator modulation efficiency is limited by electro-optic field distribution overlap and optical mode interacts with p-type dopant increases device insertion loss when Zn diffuses during MOCVD epitaxial process.

Optical insertion losses in embedded strip waveguides fabricated in LiNbO3 by Ti diffusion have been examined at a 0.633-μm wavelength, taking into account resultant near-field patterns. It is confirmed that the main factors influencing optical insertion losses are radiation loss by the deficient refractive-index change of a waveguide, scattering loss by insufficient diffused residual titanium oxide film on a waveguide, and coupling loss between a waveguide and a fiber. A diffusion condition for making a low-loss waveguide is presented, although suppression of lateral diffusion is necessary to achieve further insertion-loss reduction.

Summary form only given. Silicon photonic integrated circuits (PICs) combine dense optical system integration with industrial scalability by adopting well-established CMOS fabrication processes [1]. An electro-optic phaseshifter (EOP) represents a basic building unit of several PICs applications [1], including datacom optical switches [3], PIC-FPGAs [4], and beam steering [5]. In-situ resistive-heaters in close vicinity of waveguides [2], or free-carrier injection/depletion in doped junctions [3], are common methods to build EOPs. Literature reports thermal shifters consuming 24.7 mW to achieve DC large signal π-phaseshift [2], power consumption of injection PIN implementations [5] and depletion PN modulators [6] of 10 mW and ≈ 0 mW respectively. A thermal EOP naturally avoids carrier-induced optical insertion losses (IL), in contrast to a PIN/PN modulator. Thus, thermal and PIN/PN methods trade-off IL with electrical power rather than minimizing both [2,3]. An EOP of low optical losses and low electrical power is highly desired in large-signal, and low-speed applications [5, 7]. In this work, we propose a novel low-loss depletion type EOP. The device (Fig. 1A) utilizes a doping cross section, resembling a bi-junction transistor with both junctions reverse biased, in a rib-waveguide. While introducing implants in a waveguide adds IL, their depletion using applied voltage induces phaseshift and decreases IL [3]. Hence, using bi-junctions to increase overlapping area of the optical mode with variable depletion regions, increases induced phaseshift efficiency relative to IL, by minimizing the number of non-depleted implants overlapping with the optical mode. Figure 1B depicts 25 % increase of such overlap in the bi-junction approach relative to a conventional PN modulator under the same implant conditions. Inserting intrinsic regions between central doped area and peripheral ones leverages such higher efficiency to achieve IL of 3 dB less than a conventional NP modulator at a maximum power consumption of 0.3 nW thus preserving desired low power consumption of depletion type modulators and achieving full n-phaseshift at 4.7V. Table 1 lists simulated IL of the proposed devices using Silvaco AtlasTM and Lumerical ModeTM, as well as measurement of a conventional PN junction modulator to verify the model.

A reflow step and an improved burial procedure are demonstrated for channel waveguides formed in sol-gel glass on silicon substrates. Thick sol-gel films are deposited by repetitive spin coating and rapid thermal annealing, and etched to form ridge waveguides. Furnace heating is then used to melt both core and buffer layers simultaneously, providing a smooth surface for burial by further spin-coat deposition. Results are presented for typical core shapes, surface profiles after planarization, and optical insertion losses. >

Integrated Microwave Photonics (IMWP), which aims at the incorporation of MWP components/ subsystems in photonic circuits, is crucial for the implementation of both low-cost and advanced analog optical front-ends, thus has attracted great interest. In this research, we introduced a four-channel direct-modulated electronic-opto convertor module modulated based on Optoelectronic assembling and Packaging Technology, which integrated function blocks, i.e. RF amplifier, RF equalizer, semiconductor high-speed laser, optical lens, MCU, AD/DA, etc. in a 25-pin compact package with external SMPM and optical fiber pigtail connection. The coupling of supervision/control signals are coupled to RF/Optical components by wire-bonding and pin insulator. The implementation of internal connection methods, compared with traditional fibers and RF cables, will bring much benefit including smaller size and lower cost. Based on test results, we realized 18GHz electronic-opto modulation bandwidth with 5 dB insertion loss and <2.5 VSWR; and each channel is working at single mode status with wavelength interval around 5nm, and single mode suppression ratio better than 55 dBc. The relation between link noise figure and optical insertion loss is also analyzed.

Self-phase modulation and spectral broadening in millimeter long self-written polymer waveguide integrated with single mode fibers

A circuit design approach using cascaded structures for integrated optic modulators and switches with high extinction ratios is described and analyzed. The extinction ratios are improved by a multiplication effect and can be exceeding 30 dB for polarization independent devices with no individual voltage tuning. The trade-offs are more chip area consumption, more optical insertion loss, and a slower device response speed. These trade-offs can be minor for nonhigh speed applications, such as photonic cross-connect systems, where the switch control and crosstalk are more important issues.

Realization of sub 1 V polymeric EO modulators through systematic definition of material structure/function relationships

Traditional EO polymer modulators employ a Mach-Zehnder interferometer architecture with only one arm modulated under a microstrip line electrode. The V/sub /spl pi// of such modulator can be expressed as, V/sub /spl pi//=/spl lambda/h/n/sup 3/r/sub 33/L/spl Gamma/ (Eq. 1) where /spl lambda/ is the optical wavelength, h is the gap between electrodes, n is the index of refraction, r/sub 33/ is the EO coefficient of the polymer waveguide layer, L is the interaction length, and /spl Gamma/ is a modal overlap integral. Low V/sub /spl pi// can be achieved by adjusting one or several parameters in Eq. 1. However, many factors such as reducing the gap distance or increasing the interaction length are limited by optical insertion loss and modulation frequency requirements. The most effective approach for low V, is to increase the EO coefficient r/sub 33/, and recent work at the University of Southern California has demonstrated some limits to increasing the doping density of the nonlinear chromophores.

A new approach for attaching optical fibers to LiNbO/sub 3/ integrated optic devices is described. The all-solder approach, which uses no organic adhesives, is fast, robust, and low cost. A three-port fiberoptic gyro chip was pigtailed, and temperature cycled from 20 to 100/spl deg/C with only +//spl minus/0.5-dB change in optical insertion loss. >

Some of the most promising transmitter linearization techniques for high performance radio over fiber systems are reviewed and compared through simulation tests. Comparison is focused on Mach-Zehnder modulator (MZM) operated at low bias; MZM conventionally biased at quadrature, driven with low modulation depth and cascaded with a notch optical filter; optical single sideband and double sideband plus carrier (SSB/DSB + C); and carrier suppressed plus carrier (CS + C) methods. These transmitters are evaluated through carrier to interference ratio, optical insertion losses, and RF power penalty. The robustness to deviation from ideal transmitter settings is also assessed.