Packaged 1.5-$mu$ m Quantum-Well SOA With 0.8-W Output Power and 5.5-dB Noise Figure

We report the demonstration of a lensed-fiber- pigtailed InGaAsP–InP quantum-well semiconductor optical amplifier based on the slab-coupled optical waveguide (SCOW) concept. At a 5-A bias current and a wavelength of 1540 nm, the packaged SCOW amplifier (SCOWA) exhibits a record 0.8-W saturation output power, 13.8-dB small-signal gain, 5.5-dB noise figure, and a maximum electrical-to-optical conversion efficiency of 11%. The estimated coupling efficiency between the large (5.6 $,times,$7.5 $mu$m), fundamental SCOWA mode and the lensed fibers (6.5-$mu$ m spot size) is 90%.      

Fabrication-Tolerant Waveguide Chirped Grating Coupler for Coupling to a Perfectly Vertical Optical Fiber

We report the simulation, fabrication, and measurement results of a waveguide grating coupler that could efficiently couple light between submicrometer-sized planar waveguides and vertical optical fibers. The coupler comprises a section of chirped grating which reduces back reflection and enhances coupling efficiency. Coupling efficiency of over 34% was measured and a 3-dB bandwidth of 45 nm was obtained. An experimental study showed that the coupling efficiency was tolerant to fabrication process fluctuations which may lead to random variations in slot width and the duty cycle of the grating periods.      

Proposal for a Grating Waveguide Serving as Both a Polarization Splitter and an Efficient Coupler for Silicon-on-Insulator Nanophotonic Circuits

A grating waveguide is introduced and designed to serve as both a polarization splitter and an efficient vertical coupler between a fiber and a silicon-on-insulator (SOI) nanophotonic waveguide. Through this grating waveguide, the light from the fiber can be efficiently coupled into an SOI chip where the two orthogonally polarized waves are separated to travel towards the opposite directions along the waveguide. According to our simulations, the optimized structure can give a high coupling efficiency of about 50% for both polarizations, as well as a large bandwidth of over 70 nm and a very low polarization crosstalk below ${-}$22 dB at the output ports.      

Diplexer With Integrated Filters and Photodetector in Ge–Si Using $Gamma-{X}$ and $Gamma-{M}$ Directions in a Grating Coupler

We demonstrate a central-office-type diplexer in which the filter and photodetector are monolithically integrated on a silicon-on-insulator substrate. The photonic integrated circuit receives a 1577-nm signal from an external laser and sends it to the fiber link using a two-dimensional grating coupler. The same grating coupler receives a 1270-nm signal from the fiber link and sends it to a monolithically integrated germanium photodetector using a polarization-diversity scheme to achieve polarization independence. The grating coupler is novel in that both the $Gamma-{X}$ and $Gamma-{M}$ directions are employed. This allows the grating coupler to couple both the 1577- and 1270-nm wavelengths with a small fiber tilt angle and hence have low polarization-dependent loss.      

Milled-groove method for fiber-to-waveguide couplers

We report a simple milled-groove process integrated with a two-step ion-diffused waveguide fabrication for efficient coupling between single-mode fibers and integrated optical waveguides andY- branches. We demonstrate such a coupling technique using a) a multimode transition to single-mode waveguide coupler, and b) an integrated optical 3-dB branching waveguide coupler from a single-mode fiber to silver/sodium ion-enchanged waveguide components. The coupling loss was about 1-2 dB over a propagation length of 2 cm at an operating wavelength of 633 nm.     

Tunable Optical Dispersion Compensator Consisting of Simple Optics With Arrayed Waveguide Grating and Flat Mirror

We propose a tunable optical dispersion compensator (TODC) that uses an arrayed waveguide grating (AWG) and a flat mirror. The TODC employs simple and cost-effective optics, and its chromatic dispersion can be changed simply by translating the AWG. We obtained a 3-dB bandwidth of 39 GHz when the dispersion was tuned within 800 ps/nm, and a maximum dispersion of ${pm}$3000 ps/nm.      

Compact 90$^{circ}$ Twist Formed by a Double-Corner-Cut Square Waveguide Section

Simple and compact rectangular waveguide 90° twist is proposed. The twist transformer region is a square waveguide section with two square corner cuts. The twist full-wave model is based on the mode-matching and generalized $S$-matrix techniques. It is found that the optimized twists can provide the bandwidths of no less than 30% at the 30-dB return-loss level or 16% at the 40-dB level over a lower, middle, or higher part of the rectangular waveguide operating band. The twist lengths are five times less than the rectangular waveguide wavelength at the central frequency of the chosen operating band. Role of evanescent modes in the interaction of two small-distanced twist transitions is discussed. The design results are confirmed by the results of real device measurements.      

Widely Tunable Micro-Mechanical External-Cavity Diode Laser Emitting Around 2.1 $mu$ m

A widely tunable $(Delta lambda/lambda =7hbox{%})$ micro-mechanical external cavity GaSb-based diode laser ($mu$ ECL) emitting around 2.1 $mu$ m is presented. A micro-machined grating with a rectangular grating profile, which can be tilted electrostatically, is employed as wavelength selective element within the external cavity using a Littrow configuration. An optimized grating profile leads to a high diffraction efficiency in the ${-}1$st diffraction order and therefore to a broad tuning range of 152 nm. The maximum output power of the fiber coupled $mu$ ECL system varied only moderately between 22 and 10 mW across the tuning range.      

CPW to Rectangular Waveguide Transition on an ${hbox{LiNbO}}_{3}$ Substrate

This paper presents transition from coplanar waveguide (CPW) to rectangular waveguide for $W$ -band (75–110 GHz) operations. The waveguide consists of a cosine-shaped fin extending from the upper waveguide wall onto the CPW signal electrode. The design features direct integration of the waveguide with opto-electronic devices on lithium niobate $({hbox{LiNbO}}_{3})$ for the applications of millimeter wave to optical signal processing. Simulations and measurements show that the model works very well over the entire $W$-band. Measurements of fabricated devices have yielded return loss of more than 10 dB and insertion loss of about 2.8 dB over the operating bandwidth.      

High-Resolution Optical Sampling of 640-Gb/s Data Using Four-Wave Mixing in Dispersion-Engineered Highly Nonlinear As$_2$S $_3$ Planar Waveguides

We present the first demonstration of an optical sampling system, using the optical Kerr effect in a chip-scale device, enabling combined capability for femtosecond resolution and broadband signal wavelength tunability. A temporal resolution ${ ≪ }500$ fs is achieved using four-wave mixing in a 7-cm-short chalcogenide planar waveguide. The use of a short length, dispersion-shifted waveguide with ultrahigh nonlinearity ($10^4;{rm W}^{-1}{cdot}{rm{km}}^{-1}$) enables high-resolution optical sampling without the detrimental effect of chromatic dispersion on the temporal distortion of the signal and sampling pulses, as well as their phase mismatch. Using the device, we successfully monitor a 640-Gb/s optical time-division multiplexing (OTDM) datastream, showcasing its potential for integrated chip-based monitoring of signals at bitrates approaching and beyond Tb/s. We discuss fundamental limitations and potential improvements.      

High $Q$ -Factor Microrings Using Slightly Etched Rib Waveguides

The paper reports the design, fabrication and characterization of silicon-on-insulator (SOI) microring resonators using shallow etched rib waveguides. The variation of the $Q$-factor of microring resonators as a function of the ring diameter and coupling gap between the input waveguide and the ring is studied. Such structures are fabricated using e-beam lithography and reactive ion etching steps. Propagation loss of shallow etching rib waveguide has been evaluated to 0.8 dB/cm for wavelengths around 1550 nm. With a ring diameter of 100 $mu{rm m}$ and a coupling gap of 450 nm, the measured $Q$ -factor is 35300. These results are matched by 3-D numerical optical modeling.      

Field Trial of Duplex, 10 Gbps $,times,$8-User DPSK-OCDMA System Using a Single 16$,times,$ 16 Multi-Port Encoder/Decoder and 16-Level Phase-Shifted SSFBG Encoder/Decoders

An optical code-division multiple access (OCDMA) over wavelength-division multiplexing (WDM) system could be one promising solution to the symmetric Gigabit access network with high spectral efficiency, cost effective, good flexibility and enhanced security. A cost-effective OCDMA/WDM system using a single multi-port en/decoder at an optical line terminal (OLT) and superstructured fiber Bragg grating (SSFBG) encoder/decoders at each optical network unit (ONU) in an optical network has been proposed and demonstrated. In this paper, we prepare 16-chip, 16-level phase-shifted SSFBG encoder/decoders and develop the full-asynchronous 10 Gigabit Ethernet (10 GbE) interface OCDMA prototype for the first time. Field trials of duplex, fully-asynchronous, 10 Gbps$,times,$8-user DPSK-OCDMA system over 100 km using hybrid multi-port and SSFBG encoder/decoder are demonstrated.      

Theoretical and experimental studies of a spot-size transformerwith integrated waveguide for polarization insensitive opticalamplifiers

The simple fabrication technology of an active waveguide for polarization insensitive optical amplifiers, integrated with tapers and a passive waveguide for fiber coupling, is presented. The spot size transformation along the taper, yielding a mode expansion factor of more than 9 in horizontal direction and about 2 in vertical direction, is experimentally verified and the results are compared to theoretical computations. Using a cleaved single mode fiber, the coupling loss is as low as 2.6 dB with -1-dB positional tolerances of 2.2 μm and 1.5 μm in vertical and horizontal directions. Besides relaxing on fiber coupling, the large spot size transformation in horizontal direction allows for a drastic reduction of the reflection coefficient to less than 10^-3 at a facet tilted by 4° with respect to the waveguide axis     

Angled-Facet Spot-Size-Converter Integrated Semiconductor Optical Amplifiers Using Asymmetric Twin Waveguide Technology

The extinction ratio (defined as the difference in the optical power between 0-dB fiber-to-fiber loss and the off state level) is enhanced with the introduction of an S-bend waveguide structure using asymmetric twin waveguide techniques for a spot-size converter integrated semiconductor optical amplifier (SSC-SOA) with a polarization-insensitive offset superlattice. Angled waveguides are introduced in order to obtain low facet reflectivity without the need for antireflection coating. A curved waveguide is introduced to connect the angled and straight waveguide, minimizing their coupling loss while achieving a lateral spatial mode filter. The SSC-SOA, operating at 1.62-mum wavelength, achieves an extinction ratio up to 70 dB and a fiber-to-fiber gain of 10 dB using cleaved, flat end single-mode optical fibers.     

Effect of Si-nc to ${hbox {Er}}^{3+}$ Coupling Ratio in EDWAs Longitudinally Pumped by Visible Broad-Area Lasers

We present a finite element based model for Si-nc sensitized ${hbox {Er}}^{3+}$ doped waveguide amplifiers (EDWA), longitudinally pumped by a novel pumping scheme using broad-area visible lasers, which accurately describes the effect of the Si-nc to ${hbox {Er}}^{3+}$ coupling ratio on the amplifier performance.      

Photonic Crystal Slab Waveguides Based on Antiresonant Reflecting Optical Waveguide Structures

A novel two-dimensional photonic crystal slab waveguide based on an antiresonant reflecting optical waveguide (ARROW) structure is proposed and designed. Lightwaves propagating in this waveguide are confined by antiresonance reflection vertically and the photonic band gap laterally. In order to obtain the characteristics of the ARROW-based photonic crystal waveguides, the three-dimensional finite-difference time-domain simulations are performed. With a lateral adiabatic taper, a coupling efficiency of 80.3% from a single-mode fiber to the ARROW-based photonic crystal waveguide of a single-line defect is obtained. In addition, propagation losses less than 10 dB/mm and bend losses of 0.23 and 0.39 dB/bend for the designed 60$^{circ}$ and 120$^{circ}$ bends are achieved at an operating wavelength of $1.55~mu{hbox {m}}$.      

Low-Cost, Precision, Self-Alignment Technique for Coupling Laser and Photodiode Arrays to Polymer Waveguide Arrays on Multilayer PCBs

The first, to our knowledge, passive, precision, self-alignment technique for direct coupling of vertical cavity surface emitting laser (VCSEL) and photodiode (PD) arrays to an array of polymer buried channel waveguides on a rigid printed circuit board (PCB) is reported. It gives insertion losses as good as the best achieved previously, to within experimental measurement accuracy, but without the need for costly active alignment nor waveguide facet polishing and so is a major step towards a commercially realizable low cost connector. Such an optical connector with four duplex channels each operating at 10 Gb/s (80 Gb/s aggregate) was designed, constructed, and its alignment precision assessed. The alignment technique is applicable to polymer waveguide interconnections on both rigid and flexible multilayer printed circuit boards (PCBs). The dependence of optical coupling loss on misalignments in $x$, $y$ and $z$ of the VCSEL and PD arrays allows the precision of alignment to be assessed and its reproducibility on multiple mating cycles of the connector is reported. The first recorded measurements of crosstalk between waveguides when the connector is misaligned are reported. Lateral misalignments of the connector to within its tolerance are shown to have no effect on the signal to crosstalk ratio (SCR), to within experimental measurement accuracy. The insertion loss repeatability is similar to that of single mode fiber mechanically transferable (MT) connectors.      

$L$ -Band Polarization-Independent Reflective SOA for WDM-PON Applications

An $L$-band polarization-independent reflective semiconductor optical amplifier (RSOA) is demonstrated for the first time. Optical gain of greater than 21 dB and gain flatness better than 4 dB is achieved over the $L$-band. The polarization-dependent gain estimated using a polarization resolved spectrum is less than 1 dB over the $L$-band. The measured output saturation power is $-$1.0 dBm and the noise figure (NF) is 10 dB for the packaged device. The 3-dB frequency bandwidth for the device is 1.3 GHz making it suitable for 1.25-Gb/s modulated wavelength-division-multiplexed passive optical network networks. Further, the saturation power and the NF of the RSOA were compared with an SOA of identical length.      

A Dual-Band Self-Oscillating Mixer for -Band and -Band Applications

A self-oscillating mixer that employs both the fundamental and harmonic signals generated by the oscillator subcircuit in the mixing process is experimentally demonstrated. The resulting circuit is a dual-band down-converting mixer that can operate in $C$ -band from 5.0 to 6.0 GHz, or in $X$-band from 9.8 to 11.8 GHz. The oscillator uses active superharmonic coupling to enforce the quadrature relationship of the fundamental outputs. Either the fundamental outputs of the oscillator or the second harmonic oscillator output signals that exists at the common-mode nodes are connected to the mixer via a set of complementary switches. The mixer achieves a conversion gain between 5–12 dB in both frequency bands. The output 1-dB compression points for both modes of the mixer are approximately $-{hbox{5 dBm}}$ and the output third-order intercept point for $C$ -band and $X$ -band operation are 12 and 13 dBm, respectively. The integrated circuit was fabricated in 0.13-$mu {hbox{m}}$ CMOS technology and measures ${hbox{0.525 mm}}^{2}$ including bonding pads.      

High-Speed High-Isolation 2$, times ,$2 Fiber-Optic Switch for Wideband Radar Photonic Beamforming Controls

A new high-performance 2$, times ,$2 fiber-optic switch is designed and demonstrated for wideband radar photonic beamforming controls. The switch deploys two bulk acoustooptic deflectors (AODs) in an imaging free-space symmetric optical design that exploits image inversion control via a Dove prism to form a 2$, times ,$2 fully reversible low crosstalk noise high-speed switching structure. Experiments at the 1550-nm test wavelength show the switch to handle 0.5-W level optical input powers, $≪ {hbox{2.2-}}mu$s switching time, $≪ $2.6-dB fiber-to-fiber optical loss, better than 56-dB optical crosstalk levels, and $≪$0.2-dB polarization-dependent loss (PDL).