Division Multiplexing Applications Research Articles

DESIGN OF FFT ARCHITECTURE USING KOGGE STONE ADDER

An efficient Fast Fourier Transform (FFT) algorithm is used in the Orthogonal Frequency Division Multiplexing (OFDM) applications in order to compute the discrete Fourier transform. Also, a Single Path Delay Feedback (SDF) which is pipeline FFT architecture is used for faster performance to achieve high throughput. In conventional method, the FFT design has high delay and power due to time taken by the multiplication part. To decrease the delay, Kogge Stone Parallel Prefix Adder (KSPPA) is used with booth multiplier. As SDF is a simpler approach to realize FFT in different length, 64-point Radix-4 SDF-FFT algorithm using KSPPA in the booth multiplier is discussed in this study. The system is implemented in Xilinx 12.4 ISE and simulated using MODELSIM 6.3c. Results show that the system reduces the delay and power.

Multiple Fiber Fault Location With Low-Frequency Sub-Carrier Tone Sweep

We present a monitoring technique that can be directly integrated in the sub-carrier multiplexing (SCM) transceiver for PtP and wavelength division multiplexing and sub-carrier multiplexing passive optical networks applications. The technique is based on the detection of the backscattered signal from a baseband tone (100 Hz to 100 kHz) and interpretation with the least absolute shrinkage and selection operator (LASSO) operator, a signal processing technique which identifies the fault positions based on the mathematical model of the received signal. The proposed single-ended fiber probing method enables the location of multiple faults with no a-priori knowledge of the fiber, and offers low-cost in-service operation with negligible impact on data transmission, few meters spatial resolution, and limited dynamic range. Due to all its advantages, but also considering its reach limitation, the SincLASSO method features as an ideal monitoring candidate for short reach sub-carrier multiplexed optical fiber networks, such as the ones intended for analog mobile Fronthaul based on fiber and fiber-extended copper lines.

Experimental Demonstration of an Electro-Absorption Modulated Laser for High-Speed Transmissions at 1.55-μm Window Using Digital Signal Processing

We experimentally investigate the transmission performance of 56 Gb/s four-level pulse amplitude modulation (PAM-4) over 30-km standard single mode fiber (SMF) using a C-band EML for low-cost metro and short-reach wavelength division multiplexing (WDM) applications. Bit error rate (BER) performance below the HD-FEC threshold is achieved for up to 30-km maximum reported distance without employing dispersion compensation fiber (DCF) in the link.

Internally-loaded ring resonator configuration for optical filter applications

We study on-chip Wavelength Division Multiplexing (WDM) application of ring resonators on Silicon-on-Insulator (SOI) platform. Though WDM devices have been demonstrated earlier, there are certain challenges which are yet to be tackled. Large FSR and narrow line width requirement for a WDM device cannot be fulfilled in a conventional WDM device as the requirement for both the metrics demand opposing structural requirements from a ring resonator. A larger FSR demands for a smaller resonator length whereas smaller line width requires a large resonator length device. We overcome this using an embedded type ring resonator configuration. The structure is made of a racetrack type ring resonator with another ring embedded inside it (loading the external ring). Such structures are capable of showing coupled resonator induced transparency (CRIT) which can result in a very narrow line-width. We present initial experimental demonstration of CRIT in an internally loaded micro ring resonator fabricated on SOI material platform. The structures were optimized using 3D-FDTD analysis and coupling-matrix method.

A CMOS 90 nm 55 mW 3.4-to-9.2 GHz 12 Band Frequency Synthesizer for MB-OFDM UWB

A frequency synthesizer for ultra-wideband (UWB) multiband orthogonal frequency division multiplexing (MB-OFDM) applications is designed in TSMC 90 nm CMOS technology. It is based on two wideband PLLs (8 MHz open loop unit gain frequency) capable of settling in less than 300 ns with a 66 MHz external reference. The PLL tuning range (6.6-9.2 GHz) is extended down to 3.4 GHz by a dedicated circuit able to divide the output frequency by 1, 1.5 and 2 with a power consumption of less than 3 mW. Measured data fit the UWB MB-OFDM specifications with an integrated phase noise of 2.8RMS o at maximum output frequency and an aggregate spurious tone power of less than -27 dBc. The joint power consumption is 55 mW and the synthesizer core area occupies less than 0.5 mm2 .

New design of four-channel add-drop filters based on double-resonant cavity photonic crystals

We proposed a new double-resonant cavity four-channel add-drop filter based on the in-plane type two-dimensional (2D) photonic crystal with square lattice. Through this novel double-resonant cavity, WDM signals can be coupled in or out of the bus waveguide with 100% add-drop efficiency while completely prohibiting cross talk between the bus and the add-drop waveguides for all other wavelengths. This device could be used as an optical add-drop multiplexer (OADM) in coarse wavelength division multiplexing (CWDM) applications.

Integrated array of 1/spl times/N optical switches for wavelength-independent and WDM applications

This paper describes an optical configuration that allows effective arrangement of multiple 1/spl times/N optical switches as an integrated array. An experimental compact module of 16 arrayed 1 /spl times/ 8 optical switches, built by utilizing a cylindrical lens, achieves uniform performance and a mean fiber-to-fiber insertion loss of 2.75 dB. This paper also discusses various layouts that use the proposed optical switching module for both wavelength-independent and wavelength division multiplexing (WDM) applications.

The design, fabrication, and low-cost replication of a new type of micro-nano grating for DWDM

We describe high-efficiency gratings illuminated by incident lights in the C + L bands as the (de)multiplexers for dense wavelength division multiplexing (DWDM) application. This grating is fabricated in fused silica and replicate in polydimethylsiloxane (PDMS) and polyethylene terephthalate glycol (PETG) with the technology of nanoimprint. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1504–1507, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21719

Chirped fibre Bragg grating based multiplexer and demultiplexer for DWDM applications

A multiplexer/demultiplexer for 100 GHz channel spacing based on chirped fibre Bragg gratings with different bandwidths and optical circulators is presented. The spectral characteristics, specifications and operation of these passive devices are described, showing its potential use in dense wavelength division multiplexing (DWDM) applications.

Effect of stress on performance of dense wavelength division multiplexing filters: thermal properties.

Thin-film filters used for dense wavelength division multiplexing (DWDM) applications are processed by a variety of deposition techniques, including ion-beam sputtering. Ion-beam sputtering produces high-quality coatings and provides flexibility of coating materials. However, DWDM filters consisting of oxide films that are reactively deposited by ion-beam sputtering, as in most sputter techniques, typically exhibit high levels of compressive stress. This affects the thermal characteristics of the filters. We have identified three thermal effects: center wavelength drift with temperature, center wavelength creep, and permanent center wavelength shift. The latter two are strongly dependent on the stress state of the filter. Models are presented that support the data that were taken.

Multiple defect characterization in finite-size waveguiding photonic bandgap structures

A powerful and efficient model recently proposed by the authors based on the leaky mode propagation method is used to characterize photonic bandgap structures incorporating multiple defects, having arbitrary shape and geometrical parameter values. The importance of the defect-mode characterization in photonic bandgap materials is due to the intensive use of defects for light localization to design very promising optical devices. This paper provides a new, efficient method to model defects in waveguiding, finite-size photonic bandgap devices and analytical and closed-form expressions for the reflection and transmission coefficients and out-of-plane losses,which is very useful and easily implemented under any operating conditions. Moreover, the method has been applied to examine the capabilities of waveguiding photonic bandgap devices in dense wavelength division multiplexing filtering applications. Therefore, the design of two optical filters for such applications has been carried out and optimal design rules have been drawn using the new model.

Production and characterisation of Bragg gratings written in high-birefringence fibre optics

Bragg gratings written in high-birefringence fibre optics are a key element in the simultaneous measurement of transversal strain components and temperature, and they have several applications as single polarisation optical filters for wavelength division multiplexing (WDM) applications. Precise determination of grating characteristics is needed to aid device design, particularly taking into account the polarisation of the illuminating light. The authors report results concerning the production and characterisation of Bragg gratings in high birefringence fibre. Birefringence is measured by the wavelength dependence of the beat length, and from the Bragg grating reflection bands, for three common high birefringence fibres. Characterisation of the gratings when subjected to transversal strain and temperature is described, as well as results of the use of the grating to measure, simultaneously, those two parameters.

Tunable photonic crystal microcavities.

We present a method for tuning a photonic crystal microcavity by modulating the index of refraction of the lattice sites within and surrounding the microcavity. The index of refraction can be actively modulated after infiltrating anisotropic liquid crystals into a two-dimensional photonic crystal lattice of air cylinders in silicon. We analyze the Q-factors and resonance frequencies of a tunable photonic crystal microcavity by considering various methods of index modulation. These tunable cavities are incorporated in a channel drop filter to demonstrate their enhancement of wavelength division multiplexing photonic crystal applications.

Spectral characteristics for a fiber grating external cavity laser

A numerical investigation has been carried out on the influence of the antireflection (AR) coating of laser, the coupling efficiency of laser and fiber (η), and the reflectivity of fiber grating (R g) on the side-mode suppression ratio (SMSR) of the fiber grating external cavity laser (FGECL). The FGECL was fabricated by the assembly of the multimode Fabry–Perot (FP) laser chip and fiber grating. The results showed that the FGECL with a lower AR coating, higher η and R g exhibited a better SMSR. A comparison of the SMSR dependence on the η and R g showed that SMSR increased more rapidly with increasing η than SMSR for R g. These spectral characteristic studies of the SMSR dependence on the device parameters of the AR coating, η, and R g may provide useful device designs for the practical fabrication of a FGECL for use in dense wavelength division multiplexing (DWDM) applications.

Design and demonstration of polarization-insensitive Mach-Zehnder switch using a lattice-matched InGaAlAs/InAlAs MQW and deep-etched high-mesa waveguide structure

The authors have designed and demonstrated a 2/spl times/2 Mach-Zehnder switch in view of polarization independence as well as low propagation loss (/spl alpha/) and absorption change (/spl Delta//spl alpha/). To obtain polarization-insensitive refractive index change (/spl Delta/n), a lattice-matched InGaAlAs-InAlAs multiple quantum-well (MQW) with a large detuning wavelength was used. Moreover, to reduce the insertion loss difference between polarizations, we applied a multimode-interferometer 3-dB coupler and a deep-etched high-mesa waveguide structure. This switch, therefore, can provide polarization-independent operation about both driving voltage and insertion loss, which is indispensable to practical optical switching applications. We also paid attention to /spl Delta//spl alpha/ suppression when we decided the value of wavelength detuning and the length of the phase shift region. We also investigated the wavelength dependence of the switch. Within 1530-1560 nm, which is the erbium-doped fiber amplifier (EDFA) gain band, polarization independence in the driving voltage and the crosstalk was maintained. This result shows that the switch is also applicable in wavelength division multiplexing (WDM) applications.

A novel grating-in-etalon WDM device and a proof-of-concept demonstration of a 1 x 40 polarization insensitive WDM

We propose a novel grating-in-etalon device for wavelength division multiplexing (WDM) applications. After presenting the device concept and a specific design of the device configuration, we report a first proof-of-concept demonstration of a 1/spl times/40 polarization insensitive WDM device in LiNbO/sub 3/.

Monolithic multisegment mode-locked DBR laser for wavelength tunable picosecond pulse generation

Monolithic active/passive mode-locked DBR laser for 4/spl times/10 Gb/s optical time division multiplexing (OTDM) application at 1.55 /spl mu/m are realized by low-cost 2"-technology. The devices show excellent performance at STM-64 frequency: they deliver nearly time-bandwidth limited (<0.4) and wavelength tunable (4.3-nm range) optical return-to-zero (RZ) pulses of down to 8-ps pulsewidth.

Optical preamplifier receiver for spectrum-sliced WDM

Spectrum-slicing provides a low-cost alternative to the use of multiple coherent lasers for wavelength division multiplexing (WDM) applications by utilizing spectral slices of a single broadband noise source for creating the multichannel system. In this paper we analyze the performance of both p-i-n and optical preamplifier receivers for spectrum-sliced WDM using actual noise distributions, and the results are compared with those using the Gaussian approximation. This extends prior results of Marcuse for the detection of deterministic signals in the presence of optical amplifier and receiver noise. Although the methodology is similar, the results are considerably different when the signal is itself noise-like. For the case of noise-like signals, it is shown that when an optical preamplifier receiver is used, there exists an optimum filter bandwidth which minimizes the detection sensitivity for a given error probability. Moreover the evaluated detection sensitivity, in photons/bit, represents an order of magnitude (>10 dB) improvement over conventional detection techniques that employ p-i-n receivers. The Gaussian approximation is shown to be overly conservative when dealing with small ratios of the receiver optical to electrical bandwidth, for both p-i-n and preamplifier receivers.

Asymmetric dilation of multiwavelength cross-connect switches for low-crosstalk WDM optical networks

We predict that, for wavelength division multiplexing optical-network applications, an asymmetrically dilated configuration of a 2/spl times/2 cross-connect is significantly better in terms of overall crosstalk when the levels of the bar-port crosstalk and the cross-port crosstalk are significantly different from each other, as is the case with optical-frequency filters which utilize grating-assisted coupling. As a verification, we present a simulation study with 2/spl times/2 polarization-diversified acousto-optic tunable filters. We present a recursive method to extend the principle of asymmetric dilation to larger-size cross-connect switches, and make a recommendation for an asymmetrically dilated 4/spl times/4 cross-connect configuration.

Digitally tunable wavelength filter and laser

A novel nonmechanical, digitally tunable, polarization insensitive and optically transparent wavelength filter using holograms electro-optically written on a ferroelectric liquid crystal (FLC) spatial light modulator (SLM) has been constructed and operated to tune to discrete wavelengths spaced by 1.3 nm. The filter has been incorporated in a ring laser which is tunable over a range of 38.5 nm across the erbium window, giving output powers of 10 mW. Both wavelength filter and tunable laser are suitable for wavelength division multiplexing (WDM) applications.