Dense Wavelength Division Multiplexing (DWDM) has recently gained great popularity as it provides a cost effective way to increase the transmission capacity of the existing fiber cable plant. For a long time, Dense WDM was exclusively used for baseband digital applications, predominantly in terrestrial long haul networks and in some cases in metropolitan and enterprise networks. Recently, the performance of DWDM components and frequency-stabilized lasers has substantially improved while the costs have down significantly. This makes a variety of new optical network architectures economically viable. The first commercial 8- wavelength DWDM system designed for Hybrid Fiber Coax networks was reported in 1998. This type of DWDM system utilizes Sub-Carrier Multiplexing (SCM) of Quadrature Amplitude Modulated (QAM) signals to transport IP data digital video broadcast and Video on Demand on ITU grid lightwave carriers. The ability of DWDM to provide scalable transmission capacity in the optical layer with SCM granularity is now considered by many to be the most promising technology for future transport and distribution of broadband multimedia services.
For ultra-high-speed single media parallel interconnects, an all optical single fiber WDM format of transmitting parallel bits rather than a fiber ribbon format-where parallel bits are sent through corresponding parallel fibers in a ribbon format, can be the media of choice. Here, we shall discuss the realization of a multi-km x gbytes/sec bit-parallel WDM single fiber link. The distance-speed product of this single fiber link is more than several orders of magnitude higher than that of a fiber ribbon link. The design of a 12 bit- parallel channels WDM system operating at 1 Gbit/sec per channel rate through a single fiber will first be presented. Experimental results for a two channel system operating at that rate are given. Further improvement of distance-speed product for the BP-WDM link can be obtained with JPLs newly developed 20 Gbits/sec per channel laser diode array transmitter. Also, new computer simulation results on how a large amplitude co-propagating pulse may induce pulse compression on all the co-propagating data pulses, thereby improving the shaping of these pulses for a WDM system, will be presented and discussed. The existence of WDM solitons is also shown.
We demonstrate the high-speed operation of a wavelength- division-multiplexed optical interconnect, which is implemented by multiplexing the optical data from a multiple wavelength vertical-cavity surface-emitting laser (VCSEL) array into a single optical fiber, and demultiplexing the composite data stream using an array of resonance-enhanced photodetectors (REPD) with matching resonance wavelengths. By using VCSELs and REPDs with a quasi-planar oxide- confinement design for improved high speed performance, and using strained InGaAs/GaAs quantum wells to achieve a better trade-off between optical responsivity and wavelength selectivity, WDM operation has ben demonstrated under 1.25 Gb/s data modulation, with an optical crosstalk rejection ratio of better than -10 dB for wavelength channels that are spaced approximately 4 nm apart. The transmission performance of a single-channel, 1.0 Gb/s fiberoptic link with a 1 km span is characterized, achieving a BER equals 10-12 at a received optical signal level of -16.7 dBm. In addition, the effect of optical crosstalk from a neighboring wavelength channel, as well as the power penalty for thermally-induced wavelength de-tuning between the VCSEL and REPD have been determined.
The novel architectures of the smart optoelectronic logic gate has been proposed for the first time. In former one, both the AND and OR function can be integrate din a single circuit. These optoelectronic circuits are composed of the integrated optical waveguide directional couplers, optoelectronic converters, EDFAs, delay line, and a DFB laser. Importantly, linear device operation with low power is the main advantage as compared to the conventional optoelectronic logic elements. Moreover, characteristics of these optoelectronic circuits, such as optical path, slew- rate limiting, and phase retardation on the different states of operation, have been discussed and would be informative.
Fiber gratings have many applications in the telecommunications industry, especially in components for WDM systems. These include among others wavelength stabilizers for pump lasers, gain flatteners, add-drop modules, multiplexers, demultiplexers, dispersion compensators, ASE filters, Raman amplifiers and fiber laser sources. The many different applications require careful design and control of the fiber grating spectral response along with the use of different fabrication techniques. For the design and use of fiber gratings, consideration must be given to insertion losses, crosstalk, dispersion, temperature compensation, strength and long term reliability.
The novel structure of DWM(D)M in the applications of optoelectronics interconnects is proposed, which combines of planar optics and chirp grating. The chirp grating in the devices functions as both dispersive element and lens, which makes the device cost-effective. In this paper, grating- based WDM is intruded first. Then the novel structure of DWDM based on the combination of planar optics and chirp grating is given. The issues for designing such device are discussed next. Finally, the preliminary experimental work is given. The results show the WDM device based on this structure is promising in data communications and optoelectronic interconnects from board to board or from machine to machine.
A fully packaged dense wavelength division demultiplexer by using dispersion-enhanced volume holographic grating and V- grooved silicon fiber array is demonstrated. The device demultiplexes eight optical channels, namely at wavelengths of 1549 nm to 1536 nm every 2 nm respectively. The system insertion losses are -5.68 dB, -5.6 dB, -5.3 dB, -5.68 dB, -5.59 dB, -5.58 dB, -5.49 dB respectively. Typical adjacent cross-talks among these eight channels are less than -35dB. Epoxy and UV curing are used for fixing most parts of the optical components, which ensures the low cost of the devices. The trade-offs between getting smaller physical packaging size and linear dispersion ability at different wavelength is addressed.
A 32-channel wavelength-division demultiplexer has been designed and tested. Intended for commercial use, the instrument is designed to be rugged, stable, and insensitive to temperature variations. Operating in the 1.54-1.57-micrometers spectral range, the unit uses single-mode fiber input and multi-mode fiber output. The optics consists of a Littrow plane-grating spectrograph that uses the same lens for collimation and for focusing. In order to reduce the size of the device, the gratin is used at a large diffraction angle. A coarse ruling is used in a high diffraction order, which results in a device that has a low polarization-dependent loss. The mean insertion loss for all channels was 3.1 dB, and the standard deviation of the insertion loss was 0.23 dB. The mean channel bandwidth was 0.26 dB.
Emerging optical networks to carry burgeoning Internet traffic require many more optical components, and different types of components, than the initial point-to-point systems. 80 channel systems are very complex and require hundreds of discrete optical devices, as opposed to initial 4 channel systems, which only needed 10-20 discrete optical components. One approach to reducing the cost per function of optical components is through integration of multiple functions in a single package. Fairly complex integrated optical circuits have already been developed in the form of Arrayed Waveguide Gratings (AWG) for Dense Wavelength Division Multiplexing. In this paper we give an introduction to integrated optical circuits in the form of Planar Lightwave Circuits. Next we discuss the design and manufacturing of AWG. Then we detail the design trade-offs necessary to achieve desired system performance. Special emphasis is given to the causes of insertion loss and cross- talk, and the role of process control in manufacturing is highlighted.
Wavelength division multiplexing (WDM) is making a major impact on current high-speed optical communications and configurable network applications. Its counterpart optical time division multiplexing (OTDM) promises high-speed short pulse transmission with the fiber capacity utilized more efficiently. This paper looks at simulations of OTDM data in a time division demultiplexer. The system used to demultiplex the data is the Asymmetric Semiconductor laser Amplifier Loop Mirror (ASLALOM) which is capable of selecting high-speed optical pulses within a data train. The authors use a model of the ASLALOM which includes a time and space analysis of a traveling wave semiconductor laser amplifier. Our investigations show that this system produces crosstalk that is dependent on the data rate, which we analyzed over a range of 200 to 300 Gbit/s. Investigations also show that the crosstalk profile is dependent of the control pulse energy. We also investigate the effect of the switching window width and note two types of crosstalk are evident. The control pulse rate is varied and the effect analyzed.
Close-form expressions are used to analyze the spatial and angular linearity of the out-coupling volume holograms in wavelength division multiplexing/demultiplexing (WDM/WDDM). Optimal spatial linear out-coupling regimes are located. Some design criteria for volume holographic WDDM applicable to 800nm, 1300nm, and 1550nm optical wavelength window are addressed. As a design example, we deploy these criteria to design a passive surface normal input/output wavelength division demultiplexer working in the wavelength range of 768-864 nm. Coupling of the demultiplexed optical signal from the substrate modes to a linear multi-mode fiber array is verified with experiment. The importance of the spatial linearity of the out-coupling in volume holographic WDDM structure is highlighted and possible coupling of the signal to linear single-mode fiber array is mentioned.
High diffraction efficiency volume-holograms can still be the state of art to manipulate lightwave and have been playing important roles in optical communication and networking arena. In this paper, we will analyze several passive substrate-mode wavelength-division- multiplexing/demultiplexing structures based on these holograms. Holograms are analyzed with coupled wave theory as well as some close-form expressions, and comparisons are made along these demultiplexing structures. Normalized parameters are used to summarize the procedure for optimal designs. The generalized parameters are applicable to any optical wavelength window. The input and output coupling of optical signals by volume holograms exhibit asymmetric properties that can strongly affect the performance of the device. Coupling of the demultiplexed signals into 1D linear multi-mode fiber array is analyzed and optimized for minimum power dissipation and loss balance. Based on the analysis and with some trade-offs on several aspects of the performance, a passive 8-channel substrate-mode surface- normal input/output demultiplexer working in the wavelength range of 768-864 nm is demonstrated. Simulations are compared with experiments.
An improved fabrication process and related experiment results of an InP-based monolithic integrated transmitter OEIC with a 1.55 micrometers MQW laser diode (LD) and an InP/InGaAs heterojunction bipolar transistors (HBT) driver circuit are presented. The epitaxial structure of the laser and driver circuits were continuously grown on semi- insulating Fe-doped InP substrate by a metal-organic chemical vapor deposition system using a vertically integration. HCL, H3PO4/H2O2 and HBr/HNO3 solution system were involved as selective or nonelective wet chemical etching respectively for the epitaxies of InP, InGaAs and InGaPAs. Both a nearly-standard contact photolithography depending on a two-step exposure technique and an electrical connection related to smoothly wet chemical etching profile of InP and InGaP in the crystal direction of (01-1) were developed in the process. The laser diode with a 3-um-wide ridge waveguide forming by a double- groove process self-aligned to the metal contact of P-type region showed an average threshold current as low as about 10mA. The HBT with a 120-nm-thick base layer performed a DC current gain of about 60-70 and an emitter-collector breakdown voltage of up to 4-5V. A clear eye diagram of the monolithic transmitter under a pulsed operation with 622Mbit/s bitrate nonreturn-to-zero pseudorandom code was obtained.
The selection process leading to the development of a guest- host electro-optic material based on an amorphous polycarbonate is described. The optical loss at 1300 nm of this material system is under 2 dB/cm, which is the confidence limit of the slab measurement used. A Mach- Zehnder Modulator fabricated using the push-pull poling technique has a low switching voltage of 1.2V.
Research and engineering are being done to incorporate polymer waveguide elements within commercial-grade silica planar-lightwave circuits to enable robust thermo-optic switches and programmable attenuators as integrable components. One of the key targets for this phase of the technology is a fully-integrated, fully-reconfigurable optical add-drop module, wherein the optical dense wavelength-division multiplexers are silica arrayed- waveguide gratings with polymer thermo-optic switches and add-drop waveguide channels interposed on the same substrate for a monolithic module.
We present an electro-optic switch based on a guide-wave electro-optic beam deflector in conjunction with multiplexed waveguide holograms for wavelength-division-multiplexing applications. The presented switching device functions as a fully transparent wavelength selective cross connect for fiber optic transmission systems. The demonstrated device consists of only one driving electrode and does not require any moving component. It is capable of not only switching an optical beam but also reconfiguring many wavelengths form one fiber to many other fibers.
Proc. SPIE 3949, New technique for wavelength-division-multiplexing optical switching utilizing the mode-hopping phenomenon of semiconductor lasers in the visible wavelength region, 0000 (21 April 2000); doi: 10.1117/12.382895
We have demonstrated a novel WDM and self-routing scheme as well as electro-optical logic-gate operations based on the mode-hopping phenomenon previously considered as a cause of bad noise in the Fabry-Perot type semiconductor lasers. In our routing scheme, data signals can be sent through adequate routes because they have information on their own destinations assigned by hopped wavelengths in their carrier light wave form a laser diode. The hopped wavelength can be controlled by only switching temporarily the d.c. bias levels of the driving current of the laser diode. The performed speed of the 1XN channel wavelength-switching was estimated at about 167 nanoseconds, limited by insufficiencies in our electronics, not by the phenomenon itself. The number of destination channels 'N' has been limited to the number of allowed hopping modes in the sample laser diode. Since the mode-hopping phenomenon itself has been reported to be faster than nanoseconds, more efficient and ultra-fast self-routing or WDMA systems based on this phenomenon will be performed. In addition, we have performed electro-optical logic-gate operations by modulating the injection current of the laser diode through mode-hopping regions. The achieved data rate of our gate operations for AND, Ex-OR and NOR gates was typically 3 X 12 Mbit/s with two simultaneously modulated input signals.
With proper programming of the fiber dispersion, a new nonlinear stationary pulse called the dispersion managed soliton (DMS) can be transmitted. DMS has properties superior to the ideal optical solitons in reduction of the timing jitter caused by amplifier noise and/or interactions with other solitons. Remarkable experimental results, such as 1 Tbit/s WDM Transmission over 3,000km or 40 Gbit/s single channel transmission over 10,000km have been achieved using DMS . The talk presents a review of recent progress in DMS research both in theory and experiments and discusses their practical implementations.