Fiber-optic communication systems form the high-capacity transport infrastructure that enables global broadband data services and advanced Internet applications. The desire for higher per-fiber transport capacities and, at the same time, the drive for lower costs per end-to-end transmitted information bit has led to optically routed networks with high spectral efficiencies. Among other enabling technologies, advanced optical modulation formats have become key to the design of modern wavelength division multiplexed (WDM) fiber systems. In this paper, we review optical modulation formats in the broader context of optically routed WDM networks. We discuss the generation and detection of multigigabit/s intensity- and phase-modulated formats, and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, multipath interference, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity

Advanced Optical Modulation Formats

Al2O3 was deposited on In0.15Ga0.85As∕GaAs using atomic-layer deposition (ALD). Without any surface preparation or postthermal treatment, excellent electrical properties of Al2O3∕InGaAs∕GaAs heterostructures were obtained, in terms of low electrical leakage current density (10−8 to 10−9A∕cm2) and low interfacial density of states (Dit) in the range of 1012cm−2eV−1. The interfacial reaction and structural properties studied by high-resolution x-ray photoelectron spectroscopy (HRXPS) and high-resolution transmission electron microscopy (HRTEM). The depth profile of HRXPS, using synchrotron radiation beam and low-energy Ar+ sputtering, exhibited no residual arsenic oxides at interface. The removal of the arsenic oxides from Al2O3∕InGaAs heterostructures during the ALD process ensures the Fermi-level unpinning, which was observed in the capacitance-voltage measurements. The HRTEM shows sharp transition from amorphous oxide to single crystalline semiconductor.

Surface passivation of III-V compound semiconductors using atomic-layer-deposition-grown Al2O3

Silicon photonic devices and integrated circuits have undergone rapid and significant progresses during the last decade, transitioning from research topics in universities to product development in corporations. Silicon photonics is anticipated to be a disruptive optical technology for data communications, with applications such as intra-chip interconnects, short-reach communications in datacenters and supercomputers, and long-haul optical transmissions. Bell Labs, as the research organization of Alcatel-Lucent, a network system vendor, has an optimal position to identify the full potential of silicon photonics both in the applications and in its technical merits. Additionally it has demonstrated novel and improved high-performance optical devices, and implemented multi-function photonic integrated circuits to fulfill various communication applications. In this paper, we review our silicon photonic programs and main achievements during recent years. For devices, we review highperformance single-drive push-pull silicon Mach-Zehnder modulators, hybrid silicon/III-V lasers and silicon nitrideassisted polarization rotators. For photonic circuits, we review silicon/silicon nitride integration platforms to implement wavelength-division multiplexing receivers and transmitters. In addition, we show silicon photonic circuits are well suited for dual-polarization optical coherent transmitters and receivers, geared for advanced modulation formats. We also discuss various applications in the field of communication which may benefit from implementation in silicon photonics.

/pdf/silicon-photonic-devices-and-integrated-circuits-6wohukuihl.pdf

Silicon photonic devices and integrated circuits

New and emerging terahertz technology applications make this a very exciting time for the scientists, engineers, and technologists in the field. New sensors and detectors have been the primary driving force behind the unprecedented progress in terahertz technology, but in the last decade extraordinary developments in terahertz sources have also occurred. Driven primarily by space based missions for Earth, planetary, and astrophysical science, frequency multiplied sources have dominated the field in recent years, at least in the 2-3 THz frequency range. More recently, over the past few years terahertz quantum cascade lasers (QCLs) have made tremendous strides, finding increasing applications in terahertz systems. Vacuum electronic devices and photonic sources are not far behind either. In this article, the various technologies for terahertz sources are reviewed, and future trends are discussed.

Technology, Capabilities, and Performance of Low Power Terahertz Sources

Highly scaled indium phosphide (InP) heterojunction bipolar transistor (HBT) technologies have been demonstrated with maximum frequencies of oscillation ( $f_{\max}$ ) of >1 THz and circuit operation has been extended into the lower end of the terahertz (THz) frequency band. InP HBTs offer high radio-frequency (RF) output power density, millivolt (mV) threshold uniformity, and high levels of integration. Integration with multilevel thin-film wiring permits the realization of compact and complex THz monolithic integrated circuits (TMICs). Circuit results reported from InP HBT technologies include: 200-mW power amplifiers at 210 GHz, 670-GHz amplifiers and fundamental oscillators, and fully integrated 600-GHz transmitter circuits. We review the state of the art in THz-capable InP HBT devices and integrated circuit (IC) technologies. Challenges in extending transistor bandwidth and in circuit design at THz frequencies will also be addressed.

InP HBT Technologies for THz Integrated Circuits

Inductively coupled plasma (ICP) operated in the reactive-ion etching mode is used for mesa etching of InP using Cl2/N2 chemistry with a Ni metal mask. Etch rates of approximately 140 nm/min with very smooth and vertical sidewalls are obtained at a dc bias of 120 V. The effects of temperature, gas flow, chamber pressure, ICP source power, and substrate bias power on etch rate are studied; sidewall profile and surface morphology will be discussed.

Smooth and vertical-sidewall InP etching using Cl2/N2 inductively coupled plasma

This paper proposes a new multiport planar power-divider design by radially combining the sectorial components and the input and output matching networks. This design can achieve good input match over a wide bandwidth without resorting to transformer sections of high-impedance lines, which are difficult to realize. This approach is applied to the design of 4-and 14-way center-fed power dividers in microstrip structures with good input match (voltage standing-wave ratio (VSWR) <1.5) over a bandwidth of 30% and 15%, respectively. The return loss of output ports and the isolation among them in the 14-way divider are less than -13 dB. A simple analysis method using the radial transmission-line theory to model the microstrip sectorial components is employed to characterize the power dividers. The calculated scattering parameters are found to be in good agreement with the measured data.

/pdf/a-wide-band-multiport-planar-power-divider-design-using-3s0enddgv1.pdf

A wide-band multiport planar power-divider design using matched sectorial components in radial arrangement

Integrated push-push oscillators, achieving high output power at 210, 235 and 287 GHz, were realized in a 0.5 mum emitter double-heterojunction InGaAs/InP HBT (D-HBT) technology with a maximum oscillation frequency fmax of 335 GHz and a breakdown voltage (Vbceo) of 4 V. The oscillators are based on a balanced Colpitts topology in which a strong second harmonic signal is generated by combining the differential signals at the collector and by reactively tuning the output impedance of the oscillator using a shorted stub. Three oscillators were realized using this topology. A high-power output signal of more then 0 dBm is obtained for oscillators operating at 210 and 232 GHz, an improvement of 5 dB compared to the output power measured on an identical push-push oscillator without 2nd harmonic tuning. Close to -3 dBm output power is obtained at an output frequency of 280 GHz by further reducing the resonator length. By reducing the current, a maximum output frequency of 287 GHz is obtained.

Highly Efficient Harmonically Tuned InP D-HBT Push-Push Oscillators Operating up to 287 GHz

The power performance of GaAs MOSFETs using Ga/sub 2/O/sub 3/(Gd/sub 2/O/sub 3/) as the gate dielectric is presented. The I-V characteristics of the power devices are virtually free of hysteresis, indicating low interface state density in the oxide/GaAs interface. When operated at 850 MHz cellular frequency and tuned for maximum output power, maximum power-added efficiencies of 45 and 56% were obtained under 3 and 5 V operation, respectively. An output power of 26.5 dBm was measured from a 1 /spl mu/m/spl times/2.4 mm device under 5 V operation. These results show that the developed GaAs MOSFETs are promising candidates for microwave power amplifiers.

Ga2O3(Gd2O3)/GaAs power MOSFETs

Device encapsulation and passivation are critical for long-term reliability and stability. Several encapsulation techniques were evaluated in terms of degradation of electrical characteristics, gap filling under the mesa structures, and adhesion to the semiconductor and metal surfaces. These included plasma enhanced chemical vapor deposited (PECVD) SiO2, electron cyclotron resonance CVD SiNx, spin-on glass, benzocyclobutene, and polyimide. Damage from plasma exposure caused gain degradation in the devices. Spin-on coatings cause little to no gain degradation, provided that there is minimal stress in the cured film. SOG and BCB films have acceptable adhesion properties and were excellent for gap filling. Polyimide films have excellent adhesion properties, however, they were poor at gap filling and had a great deal of shrinkage during curing. Device passivation was evaluated using double heterojunction bipolar transistor structures with either an abrupt or graded emitter-base junction. Abrupt junction devices had the self-aligned base metal directly on the p+ InGaAs base. Graded junction devices had the base metal on top of graded InGaAsP layers, which the metal was diffused through, to make contact to the base region. Abrupt junction devices stressed at an initial JE of 90 kA/cm2 at a VCE of 2V at 25°C degraded 20% within 70 h of operation, whereas, the graded junction devices show no degradation in dc characteristics after operation for over 500 h. Typical common emitter current gain was 50. An ft of 80 and fmax of 155 GHz were achieved for 2×4 µm2 emitter size devices.

Y.K. Chen

Papers

Smooth and vertical-sidewall InP etching using Cl2/N2 inductively coupled plasma

A wide-band multiport planar power-divider design using matched sectorial components in radial arrangement

Highly Efficient Harmonically Tuned InP D-HBT Push-Push Oscillators Operating up to 287 GHz

Ga2O3(Gd2O3)/GaAs power MOSFETs

Evaluation of encapsulation and passivation of InGaAs/InP DHBT devices for long-term reliability