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The emerging applications for inter and intradata center communications demand low-cost and small-from-factor optical transceivers with 100G/400G capacity. Various techniques, such as wavelength-division multiplexing (WDM), multilevel pulse-amplitude modulation, and discrete multitone (DMT), are heavily investigated in this field. Among these techniques, DMT can offer 100G capacity with 10–20G optical devices using direct detection, which provides a very promising low-cost 100G/400G solution. In this paper, we report silicon photonic four-channel DMT integrated circuits, which demonstrate net channel rates of 70 and 100 Gb/s detected by integrated germanium receivers and commercial receivers, respectively. The silicon photonic chip integrates four silicon Mach–Zehnder modulators and WDM multiplexers using thermally tuned second-order microring filters. Besides the wavelength multiplexing functionality, we also demonstrate that these microrings can serve as vestigial sideband filters to enhance the transmission performance in 20–40 km ranges. These demonstrations indicate the promise of using low-cost and high-integrated silicon photonic circuits in high capacity 100G/400G applications.

Silicon photonics has technical advantages allowing for large-scale optical integrated circuits due to both the nature of high-index-contrast silicon waveguides and the mature fabrication processes. Recent advances in this field have shown remarkable monolithic integration capabilities for both passive and active optical components on the same chip. In this paper, we report an in-phase/quadrature modulator with on-chip optical equalizer in a silicon photonic circuit, capable of generating 56-Gbaud quadrature-phase-shift-keyed signals. The equalizer provides 2.5-dB improvement in optical signal-to-noise ratio at a bit-error ratio of $2.4 \times 10^{-2}$ .

We present silicon photonic integrated circuits (PICs) based coherent optical transmitters and receivers for high-speed long-distance fiber optical transmission. High-degree photonic integration is achieved by monolithically integrating silicon electro-optic modulators, germanium photo detectors, silicon nitride-assisted on-chip polarization rotators, thermal phase shifters, and various passive silicon optical devices on a single wafer platform. We demonstrate the use of these PICs for modulating and detecting 112-Gb/s polarization-division-multiplexed quadrature phase-shift keying (PDM-QPSK) and 224-Gb/s PDM 16-ary quadrature amplitude modulation (PDM-16-QAM) signals. Transmission and coherent detection of a 112-Gb/s PDM-QPSK signal over 2560-km standard single-mode fiber is also demonstrated. The high-degree photonic integration for silicon PICs promises small-form-factor and low-power-consumption transceivers for future coherent systems that demand high cost efficiency and energy efficiency.

We present a quasi-real-time coherent sampling approach that combines the high-bandwidth and high-fidelity signal acquisition of equivalent-time optical sampling with real-time digital signal processing and equalization algorithms. The quasi-real-time concept enables feasibility studies of optical communication at symbol rates beyond the bandwidth of conventional digitizer approaches. Here we demonstrate the technique using a 107-GBd polarization-division-multiplexed quadrature phase shift keyed signal.

We present a reconfigurable optical discriminator filter for frequency modulated microwave-photonics link applications. The filter is based on a simplified ring-assisted Mach-Zehnder interferometer configuration. It enables conversion of a highly linear frequency to amplitude modulation. Operations in a fixed bandwidth (BW) of 30 GHz and a tunable bandwidth from 10 to 30 GHz are achieved using third- and fifth-order filters. A balanced frequency discrimination architecture with electronically reconfigurable transfer characteristics is demonstrated. We measured a output-third order intercept point (OIP3) linearity improvement over that of a dual-output Mach-Zehnder.

We propose and demonstrate all-optical method for generating advanced modulation formats with high-spectral efficiency. The proposed method is based on all-optical format conversion using photonic-integrated semiconductor optical amplifier-Mach-Zehnder interferometers. It enables application of advanced modulation formats at data rates not directly accessible using electronic means only. We demonstrate generation of single-polarization 86.4-Gb/s binary phase-shift keying and 173-Gb/s quadrature phase-shift keying optical signals.

We describe in further detail a demonstration of a monolithic 1 × 2 silicon wavelength-selective switch in silicon photonics. The switching has a flexible grid with 32 pixels on a pitch of 100 GHz. It is extremely compact, being only 3.0 × 5.5 mm2, and it can potentially be mass-produced by a silicon foundry. It requires improvements in many characteristics, though, most notably insertion loss, resolution, and pixel count.

We describe in more detail a novel InP-based comb generator for optical orthogonal frequency division multiplexed (OFDM) transmission. The device integrates a Mach-Zehnder interferometer inside an amplified ring. In order to maximize the number of lines in the spectrum, the phase modulators were designed with a 3-step asymmetric quantum well structure to maximize the index change with voltage change. We demonstrate a 6-line frequency comb which is tunable over 80 nm. The linewidth of the comb is limited by only the input laser, which makes this device especially suitable for coherent optical OFDM applications.

We discuss the generation, wavelength-division-multiplexed (WDM) long-haul transmission, and coherent detection of 112-Gb/s polarization-division-multiplexed (PDM) 16-ary quadrature amplitude modulation (16-QAM) at a line rate of 14 Gbaud and spectral efficiencies beyond 4 b/s/Hz. We describe the (off-line) digital signal processing and blind filter adaptation algorithms used in our intradyne receiver and characterize its performance using both simulated and measured 16-QAM waveforms. We measure a required optical signal-to-noise ratio of 20.2 dB (0.1-nm reference bandwidth; 10-3 bit-error ratio), 3.2-dB off the theoretical limit. We study the effects of finite analog-to-digital converter resolution, laser frequency offset, laser phase noise, and narrowband optical filtering. Our experiments on a 25-GHz WDM grid (4.1-b/s/Hz spectral efficiency) reveal a 1-dB penalty after 7 passes though reconfigurable optical add/drop multiplexers (ROADMs) and an achievable transmission reach of 1022 km of uncompensated standard single-mode fiber. At a spectral efficiency of 6.2 b/s/Hz (16.67-GHz WDM channel spacing) a transmission reach of 630 km is attained.

We discuss the generation, detection, and long-haul transmission of single-polarization differential quadrature phase shift keying (DQPSK) signals at a line rate of 53.5 Gbaud to support a net information bit rate of 100 Gb/s. In the laboratory, we demonstrate 10-channel wavelength-division multiplexed (WDM) point-to-point transmission over 2000 km on a 150-GHz WDM grid, and 1200-km optically routed networking including 6 reconfigurable optical add/drop multiplexers (ROADMs) on a 100-GHz grid. We then report transmission over the commercial, 50-GHz spaced long-haul optical transport platform LambdaXtremereg. In a straight-line laboratory testbed, we demonstrate single-channel 700-km transmission, including an intermediate ROADM. On a field-deployed, live traffic bearing Verizon installation between Tampa and Miami, Florida, we achieve 500-km transmission, with no changes to the commercial system hardware or software and with 6 dB system margin. On the same operational system, we finally demonstrate 100-Gb/s DQPSK encoding on a field-programmable gate array (FPGA) and the transmission of real-time video traffic.

We present experimental investigations of the dynamical properties of semiconductor optical amplifiers (SOAs) and their impacts in all-optical signal processing using SOAs. We introduce ultrafast optical signal characterization techniques to fully characterize the gain and phase dynamics of SOAs. We elucidate a consequence of the slow carrier recovery as pattern-dependent phase fluctuation in wavelength conversion of on-off -keyed signals. We also analyze the conversion of the phase fluctuation into amplitude fluctuation limiting the performance of all-optical xor operation. Finally, the performance of all-optical wavelength conversion of differential phase-shift-keyed signals is presented with emphasis on regeneration of the phase information.

A novel 16-channel digitally wavelength-tunable laser is proposed and experimentally demonstrated using a semiconductor optical amplifier and silicon photonic integrated circuit. The device exhibits a laser threshold below 45 mA, SMSR around 20–25 dB and nanosecond switching time.

We report four-channel discrete multi-tone modulation at 100G per channel using silicon photonic integrated circuits. Second-order rings are used for both wavelength multiplexing and vestigial sideband filtering to enhance the transmission performance in 20–40 kilometers.

An all-optical switchable wavelength-converting module at 40 Gb/s line rate is demonstrated in a fully integrated InP chip. The device combines a semiconductor optical amplifier-based wavelength converter and a fast-tunable multifrequency laser. Sub-nanosecond switching among the eight channels of the integrated laser is shown, and error-free operation of the wavelength conversion process at 40 Gb/s for each wavelength is demonstrated. The applications of fast switching wavelength conversion for optical switching and packet routing are discussed.

Highly versatile building blocks for polarization-mode dispersion (PMD) emulation and compensation are demonstrated using tunable all-pass filters fabricated in 4%-index-contrast planar waveguides. While the all-pass filters can approximate any phase response, the complexity in setting the individual filter parameters is minimized by restricting the all-pass filter responses to realize a range of differential delays, dispersion, and dispersion slope. A single section can approximate first-order or a higher-order PMD term or emulate chromatic or higher-order dispersion. A differential group delay (DGD) tuning range over 100 ps is demonstrated for 10 Gb/s and 25 ps for 40 Gb/s data. Second-order PMD with a tuning range of 255 ps/sup 2/ and third-order PMD with a range of 2430 ps/sup 3/ are also demonstrated. The larger index contrast required for the ring-resonator-based all-pass filters is advantageous in reducing the thermooptic response time to achieve polarization rotation speeds on the order of 0.1 /spl mu/s/degree. The device is interferometrically stable and compact in size. It can be fully integrated, scaled to many sections, and can implement a variety of PMD synthesis and statistical-emulation approaches.

Compact parallel transmitters and receivers with an aggregate capacity of 107 Gb/s are built through hybrid integration of arrays of ten 100-GHz spaced directly modulated lasers, arrays of ten avalanche photodiodes, and high-index contrast silica arrayed waveguide grating multi- and demultiplexers. Unamplified transmission over 75 km of standard single-mode fiber and 155-km amplified links is demonstrated in the C-band, by using a modulation format based on spectral offset filtering and electronic dispersion compensation.

A single-carrier 640-Gb/s polarization-division multiplexed 16-ary quadrature amplitude modulation signal is generated using electronic multiplexing to 80 Gbaud. Coherent detection and off-line signal processing equalize the limited bandwidth of the transmit and receive hardware.

We demonstrate a novel polarization-division multiplexed differential quadrature phase-shift keying receiver. It has the minimum number of analog controls and an integrated polarization interference monitor for polarization tracking. It can theoretically tolerate polarization-dependent loss in the link. We achieve ~10 times tracking speed improvement, ~6-dB lower loss, and ~100 times lower average bit-error rate during most of the tracking over our previous work for 43-Gb/s PDM-DQPSK.

A single-polarization 160-Gb/s (80-Gbaud) electronically time-division-multiplexed (ETDM) quadrature phase-shift-keyed (QPSK) signal is generated and coherently detected using two 45-GHz-bandwidth oscilloscope prototypes and offline processing.

We demonstrate a monolithic eight-channel coarse wavelength-division-multiplexing (CWDM) receiver. It has a spot-size converter in SiO2 and Si3N4, an arrayed-waveguide grating (AWG) in Si3N4, fan-out waveguides in Si, and photodetectors in Ge. By appropriately varying the waveguide widths in the AWG, polarization independence is achieved. The responsivity from fiber to photodiode for the best channel is higher than 0.34 A/W over all polarizations. We demonstrate -20.3-dBm sensitivity at 10-12 bit-error rate at 2.5 Gb/s for one of the channels using a commercial small-form-factor pluggable (SFP) transceiver as a transmitter.

We transmit 40-Gb/s optical packets through a load-balanced optical packet router consisting of two 16 × 16 arrayed waveguide gratings, wavelength converters, and an optical-time buffer. The optical router interoperates with an electronic router with 10-GbE interfaces.

We describe a polarization-insensitive two-channel receiver which utilizes a novel Mach-Zehnder interferometer on a high-index-contrast waveguide platform and integrated germanium photodetectors for access application. A fiber-to-detector polarization-dependent loss of less than 0.8 dB is demonstrated over a wide wavelength range. By packaging the receiver chip with transimpedance amplifiers, we measured sensitivities of -23.3 and -22.6 dBm for the two channels at 2.5 Gb/s and demonstrated polarization-insensitive operations.

Using a Si photonic integrated circuit and separate SiGe transimpedance amplifiers, we created a high-performance dual-polarization, dual-quadrature coherent receiver. It requires only 16.3-dB optical signal-to-noise ratio to receive a 112-Gb/s polarization-division-multiplexed quadrature phase-shift keying signal at a 10-3 bit-error rate.

We propose an optical interleaver using an arrayed waveguide grating-lens-grating cascade and a 3-dB coupler. It has a narrow channel spacing, high-order Gaussian passbands, and low chromatic dispersion. We demonstrate a 16.7-GHz version for spectrally efficient wavelength-division-multiplexed systems.

In 2005, Griffin showed that an InP phase-shift-keying/duobinary Mach-Zehnder interferometer (MZI) modulator could achieve good transmission performance at 10 Gb/s, despite modest residual amplitude modulation in the phase modulators in the MZI (ratio of real to imaginary part of index change was ~0.1). Here we show that even strong amplitude modulation in the ldquophaserdquo modulators (ratio of real to imaginary part of index change is ~1.0) gives good transmission performance. Allowing for strong amplitude modulation allows a significant increase in modulator bandwidth. We demonstrate low-chirp 85.4-Gb/s optical duobinary generation in a fully packaged InP photonic integrated circuit.

We demonstrate all-optical recognition of a byte pattern embedded in phase-shift-keyed data streaming at 40 Gb/s. We use matched filtering to generate an autocorrelation pulse indicating the pattern matching. Matched filtering is implemented using a reconfigurable silica planar-lightwave-circuit optical delay-line filter. We show excellent discrimination against spurious patterns consistent with the theoretical predictions.

We describe a simple method to measure the optical signal-to-noise ratio (OSNR) of on-off-keying (OOK) and differential phase-shift-keying (DPSK) signals by using an optical delay interferometer (ODI) having a sinusoidal and tunable passband. This OSNR monitoring method is independent of chromatic dispersion, polarization-mode dispersion, and noise polarization. We show experimentally that accurate OSNR measurements are made for a 10-Gb/s OOK signal by using a 1-bit ODI and a 40-Gb/s DPSK signal by using a partial-bit ODI with the OSNR ranging from 5 to 25 dB.

By using a novel multisection three-waveguide directional coupler, we significantly improve the performance of a passband-flattened arrayed waveguide grating router that uses a three-arm interferometer connected to the input. Each passband has three low-loss maxima. For a 16-channel demultiplexer, we achieve a 1- to 20-dB passband-width ratio of 0.62 and a fiber-to-fiber insertion loss of 2.5-3.6 dB

Polarization crosstalk in planar lightwave circuit directional couplers can cause significant polarization-dependence in interferometers that use them. We show a simple way to mitigate the polarization crosstalk without incurring a performance penalty or requiring extra fabrication steps. We demonstrate it on a 23-ps Mach-Zehnder delay interferometer

The small form factor chirp-managed laser (CML) source at 1550 nm was used in conjunction with postdetection electronic signal processing to successfully achieve transmission over 1200 km of nonzero dispersion-shifted fiber in a dense wavelength-division-multiplexing environment, without using any optical dispersion compensation. In a comparative study, the dispersion tolerance and the transmission performance of the CML were found to be better than the duobinary format.

We describe a method to study dense wavelength-division multiplexed (DWDM) transmission over amplified links that have no inline dispersion compensation and where the channels have nearly 100% precompensation. The approach is based on two recirculating loops that are linked to each other. Using this apparatus, we demonstrate DWDM transmission of 16 nonreturn-to-zero 10-Gb/s channels on a 50-GHz grid over links ranging from 320 to 1280 km of standard single-mode fiber with precompensation values ranging from -5440 to -21 760 ps/nm.

We present a monolithic polarization diversity coherent receiver by employing 120-degree optical hybrids on a silicon photonic integrated circuit (PIC). This PIC monolithically integrates silicon inverse tapers for fiber coupling, silicon polarization splitters, germanium high-speed photo detectors, and 120-degree optical hybrids based on 3x3 multimode interferometers (MMI). We demonstrate that 112-Gb/s polarization-division-multiplexed quadrature phase-shift keyed signals are detected in the wavelength range of 1530-1580 nm with comparable performance to commercial receivers.

We demonstrate a record repeaterless transmission distance of 285 km over standard single-mode fiber at 10.664 Gb/s. A span loss of 60 dB with a total dispersion of 4850 ps/nm were simultaneously overcome using a chirp managed laser. High launch power coupled with low extinction ratio are shown to be key parameters in achieving long unrepeatered links.

We previously demonstrated a colorless three-stage Mach-Zehnder-interferometer-type 10-Gb/s tunable dispersion compensator (TDC) in a silica-on-silicon planar lightwave circuit. However, the bandwidth was too narrow to tolerate typical transmitter wavelength drift. Here we demonstrate a wider bandwidth version, in which we increased the TDC free-spectral range (FSR) and put two TDCs in series onto the same chip. Key features are that a single voltage tunes the entire device, and a single half-wave plate makes the entire device polarization insensitive. This 50-GHz FSR device allows 180 km of 9.95-Gb/s transmission. We also demonstrate a 100-GHz FSR version, which compensates /spl sim//spl plusmn/200 ps/nm of 42.7-Gb/s transmission.

Novel five-band 8-skip-0 band filters realized in silica waveguide planar lightwave circuit technology were successfully used to demonstrate versatile wavelength-division-multiplexed (WDM) optical networking. Forty C-band channels spaced 100 GHz apart grouped in five bands of eight channels each allowed WDM networking without loss of any channel within the available optical bandwidth. We demonstrate simultaneous transport of 10 and 40 Gb/s with rate-appropriate optical add-drop nodes.

We report a hierarchical optical add-drop multiplexer (OADM) network that supports 10-, 40-, and 160-Gb/s data rates with the same bandwidth efficiency. The data rates can be upgraded without hardware modification in the OADM. This hierarchical OADM network is equipped with high capacity (1.6 Tb/s) for traffic growth, while providing different granularities for diverse bandwidth requirements as fine as 12.5 GHz in optical domain. We investigate the transmission penalty through the waveband OADMs, and compare the performance between all-through traffic and add-drop traffic of neighboring wavebands at 40-Gb/s rate.