Optical Data Signals Research Articles

A vision chip with column-level amplification of optical data signals for indoor optical wireless local area networks

We present a vision chip architecture with column-level photo-amplification of optical data signals for optical wireless local area networks (LANs) to reduce the pixel area. Based on the architecture, we have fabricated a prototype vision chip in a standard 0.8 μm bipolar complementary metal-oxide-semiconductor (BiCMOS) technology. The device offers position detection of other optical transceivers in the LAN and 4-ch concurrent high-speed optical data acquisition. A data rate of 400 Mbps was demonstrated. The pixel size was 125 μm square, which can be shrunk to smaller than around 60 μm square in 0.35 μm or more advanced BiCMOS or CMOS technologies.

Plasmonic all-optical tunable wavelength shifter

At present, wavelength-division-multiplexed fibre lines routinely operate at 10 Gbit s−1 per channel. The transition from static-path networks to true all-optical networks encompassing many nodes, in which channels are added/dropped and efficiently reassigned, will require improved tools for all-optical wavelength shifting. Specifically, one must be able to shift the carrier wavelength (frequency) of an optical data signal over tens of nanometres (a THz range) without the bottleneck of electrical conversion. Popular approaches to this problem make use of the nonlinear interaction between two wavelengths within a semiconductor optical amplifier1 whereas more novel methods invoke terahertz-frequency electro–optic modulation2 and polaritons3. Here we outline the principles and demonstrate the use of optically excited plasmons as a tunable frequency source that can be mixed with a laser frequency through Raman scattering. The scheme is all-optical and enables dynamical control of the output carrier wavelength simply by varying the power of a control laser.

Raman amplification of 40 Gb/s data in low-loss silicon waveguides

We demonstrate on-chip Raman amplification of an optical data signal at 40 Gb/s in a silicon-on-insulator p-i-n rib waveguide. Using 230 mW of coupled pump power, on/off gain of up to 2.3 dB is observed, while signal integrity is maintained. In addition, the gain is measured as a function of signal wavelength detuning from the Stokes wavelength. The Lorentzian linewidth of the Raman gain profile is determined to be approximately 80 GHz. This provides applicability for the selective amplification of individual DWDM optical channels.

On intranode impairments and engineering rules for an optical label switching router supporting an FSK/IM labeling scheme

This paper presents a study on intranode impairments and engineering rules for a label switching router supporting intensity modulated (IM) optical payload data signals labeled by using frequency-shift key (FSK) modulation. Engineering rules and design guidelines are presented regarding the choice of system parameters such as IM extinction ratio, FSK frequency deviation, alignment of optical filtering stages, label swapping, and node cascadability. The presented rules are derived from insights obtained from computer simulations and experimental validation for a 10-Gb/s IM payload signal

Optical sampling techniques

The optical sampling technique is a novel method to perform time-resolved measurements of optical data signals at high bit rates with a bandwidth that cannot be reached by conventional photodetectors and oscilloscopes. The chapter reviews the techniques that are used in optical sampling systems to perform the ultrafast sampling of the signal under investigation. In addition to the various nonlinear materials and effects used for the optical sampling gates and pulse sources, the realized optical sampling systems also differ in the way, in which the system is synchronized to the data signal. Systems have been reported using synchronous, random and software synchronized configurations. Applications of optical sampling systems include high bit rate waveform and eye diagram measurements, measurements of constellation diagrams of phase modulated data signals, time-resolved measurements of the state-of-polarization as well as investigations of fiber transmission impairments.

Optical clock recovery circuits using traveling-wave electroabsorption modulator-based ring oscillators for 3R regeneration

We describe an optical clock recovery circuit that employs a traveling-wave electroabsorption modulator-based ring oscillator. This approach provides synchronized optical clock and the original optical data signal from the same output at separate wavelengths, eliminating additional timing adjustments for the subsequent nonlinear decision gate for reamplifying, reshaping, and retiming (3R) regeneration. Furthermore, additional retiming and lateral reshaping of the original data signal can be realized along with optical clock recovery by synchronized modulation. We present a general model of jitter transfer and locking dynamics for the clock recovery circuit and compare with experimental results. Theoretical results indicate that by using hybrid integration to shorten the cavity length, nanosecond-order locking time can be achieved, which is critical for a variety of applications such as protection switching, optical burst and optical packet switching. Experimental demonstrations of 40-Gb/s optical clock recovery and its application for optical 3R regeneration are presented. The recovered 40-GHz optical clock has 500-fs timing jitter and 8-ps pulsewidth, and within 0.3 /spl mu/s locking time. 3R experiment is implemented by using the OCR combined with a subsequent regenerative wavelength converter, which provides vertical reshaping function. 3R regeneration is demonstrated with a reduced timing jitter.

Optical performance monitoring using narrowband radio-frequency analysis at the half-clock frequency

Feature Issue on Optical Performance Monitoring (OPM). A new technique for monitoring the signal-to-noise ratio (SNR) of a randomly modulated optical data signal is proposed and demonstrated. The signal is detected and then subjected to a narrowband rf demodulation at precisely half the data clock frequency. Because of symmetries present in the modulation spectrum at the half-clock frequency, the demodulated signal is confined to a single dimension in the recovered phase space. In contrast, the noise power is distributed isotropically within the phase space, and the SNR is measured by taking the ratio of the power recovered along the signal dimension to the power recovered along the orthogonal dimension. The narrowband nature of the measurement makes it highly sensitive. The technique is demonstrated for return-to-zero modulated data at 10 Gbits/s, where it accurately tracks OSNR variations from 10 to 26 dB with only -24 dBm of optical input. The measurement is also shown to be sensitive to chromatic dispersion and can be made to track OSNR variations in the presence of large amounts of chromatic dispersion with vestigial sideband optical filtering. These properties make this technique an ideal candidate for optical performance monitoring in transparent optical networks, where a sensitive, low-cost monitoring solution is needed for effective fault localization.

All-optical coding of mode-locked semiconductor laser pulse trains for high bit rate optical communications

We demonstrate an all-optical scheme for coding high frequency mode-locked semiconductor laser pulse trains. The scheme is experimentally demonstrated by optically modulating a high frequency pulse train at 38 GHz generated by a subharmonic synchronous mode-locked semiconductor laser with binary information contained in multiple low bit rate optical data signals (3.8 Gb/s). Synchronization between the two signals is achieved through optical injection into the mode-locked laser while high speed modulation is achieved via a nonlinear optical loop mirror made of dispersion shifted fiber. The coding scheme has advantages over existing passive multiplexing schemes in generating high data rate optical signals due to its regeneration and wavelength conversion functionality.

Method for PMD vector monitoring in picosecond pulse transmission systems

A method and a device are proposed that allow measurement of the polarization mode dispersion (PMD) in a transmission line without data traffic interruption. The PMD vector information is extracted from the optical data signal spectrum. The method is experimentally verified by measuring of first-order PMD.

Self-pulsating DFB laser for all-optical clockrecovery at 40 Gbit/s

A first demonstration of a 40 Gbit/s all optical clock recovery module based on a design for a novel self-pulsating DFB laser is presented. The role of detuned gratings in the new device concept is evaluated and experimental results of self-pulsation at 40 GHz are reported. The successful locking to 40 Gbit/s optical data signals emphasises the future application in an all-optical 3R-regenerator.

Ultra-fast optoelectronic circuit usingresonant tunnelling diodes and uni-travelling-carrier photodiode

An ultra-fast optoelectronic circuit, using resonant tunnelling diodes (RTDs) and a uni-travelling-carrier photodiode (UTC-PD) is proposed. At extremely low power consumption, the circuit can demulitiplex an ultra-fast optical data signal into an electrical data signal with a lower bit rate. The monolithically fabricated circuit demultiplexed an 80 Gbit/s optical signal into a 40 Gbit/s electrical signal at 7.75 mW.

Versatile fibre laser mode-locked by an optical data signal

We demonstrate experimentally a versatile fibre ring laser. When all-optically mode-locked by a data signal the fibre laser can generate either a copy of a repetitive data signal, a recovered optical clock, or a recovered frame synchronization signal. We propose to use the recovered frame synchronization signal in a novel true all-optical demultiplexer.

All-optical remote switching for multiplexed optical fiber sensors and communications systems

All-optical self-routing switches are described which automatically route optical data signals. These switches require no separate source of power, and have been demonstrated to operate from a single input laser beam of 300 /spl mu/W. The input laser beam contains the data, destination address, and optical power. These optical switches can be used for all-optical communication systems, and are used as an example in this paper to demonstrate remote switching via an optical fiber to a sensor. The sensor modulates the optical carrier which returns the modulated carrier to the source end of the fiber. The switch demonstrates auto-aligning properties which ensure correct rerouting of the modulated signal back to the source. Operation has been demonstrated for all the visible lines of an argon ion laser.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical architectures modeling: A new methodology

In this paper, we devise a methodology for optical component modeling. We present the general description of single-port and multi-port optical components. Then we use signal flow graphs to analyze optical architectures prior to the implementation phase. It illustrates the behavior of the optical data signal at the output of the optical system.

20 Gbit/s, 1020 km penalty-free soliton data transmission using erbium-doped fibre amplifiers

Optical soliton data signals at 20 Gbit/s have been successfully transmitted for the first time over a 1020 km-long dispersion-shifted fibre. Erbium-doped fibre amplifiers were installed as optical 1R repeaters at every 50 km. A bit error rate of below 10/sup -12/ was obtained with 2/sup 23/-1 pseudorandom patterns under a penalty-free condition. >

All-optical clock recovery from 5 Gb/s RZ data using a self-pulsating 1.56 mu m laser diode

All-optical clock extraction from 5 Gb/s RZ data is demonstrated using a two-contact InGaAsP semiconductor self-pulsating laser diode. The saturable absorber region of the device was doped with zinc ions to reduce the carrier lifetime in this region such that strong self pulsations at frequencies up to 5.2 GHz were obtained. Injection of a 10- mu W optical data signal at a wavelength close to one of the Fabry-Perot wavelengths was sufficient to synchronize the self pulsations to the incoming data stream. The measured 3-dB RF electrical bandwidth of the synchronized optical clock signal was 10 Hz, approximately the same as that of the electrical transmitter clock. Initial bit-error-rate measurements for 2/sup 7/-1 5 Gb/s data result in a 0.5-dB receiver sensitivity penalty when using the optical clock signal compared to the transmitter clock. >

All-optical frequency conversion in a traveling-wave semiconductor laser amplifier

All-optical frequency conversion over the entire gain spectrum of a traveling-wave semiconductor laser amplifier is analyzed by numerical solution of a nonlinear wave equation system. The wavelength dependence of the gain coefficient g, the linewidth enhancement factor alpha , the differential gain dg/dN, and the gain saturation effect are contained in the model. The method yields a high conversion efficiency and a converted signal output power up to 10 dBm is obtainable. It is shown that the input signal power can vary by three orders of magnitude with nearly no degradation of the conversion efficiency. By means of the input powers, the conversion efficiency can be maximized. The dependence of the conversion efficiency is analyzed for fixed input powers. Simultaneous conversion of an optical data signal to several wavelengths is analyzed. The requirements for the output filter are outlined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Frequency conversion by nearly-degenerate four-wave mixing in traveling-wave semiconductor laser amplifiers

The paper describes a scheme for frequency conversion of optical data signals with use of NDFWM in travelling wave semiconductor laser amplifiers. The frequency conversion range is limited by the gain bandwidth of the optical amplifier, which is about 4000 GHz in the considered case. The experimental arrangement of the conversion scheme is described and a theoretical analysis is presented. Finally the advantages and disadvantages of this scheme are discussed.

Optically powered optical interconnection system

A wavelength-multiplexed optical interconnection system in which the electrical power is provided by an optical source is discussed. The optical power and data signals, operating at two different wavelengths, are multiplexed onto a single fiber at the local terminal, and demultiplexed at a remote terminal. The optical power is then converted to electrical power by an array of photovoltaic cells, providing bias control to a data-detection circuit. The system operates at 45 Mb/s, the remote receiver dissipates 2.6 mW, and there is negligible optical crosstalk between the power and data channels.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Semiconductor-laser amplifier as an optically controlled switch

The application of a semiconductor-laser amplifier with reduced facet reflectivity as all-optical switch is described. An optical data signal is switched on and off with an extinction ratio of 10 dB when an optical control signal is turned on and off. The two optical signals are polarized perpendicularly to each other. The device was operated up to 100 MHz.