A review is presented of state-of-the-art optical planar waveguide demultiplexers (DEMUXes); that is, phasars (arrayed waveguide) and etched grating devices designed for high density (narrow channel spacing) wavelength division multiplexing (WDM) systems. Their advantages and disadvantages are discussed in comparison with other techniques for demultiplexing WDM signals. The advances made in their performance are reviewed and ultimate limitations, set by technological constraints, are proposed. Finally, a comparison is made of the advantages and disadvantages of etched grating as opposed to phasar planar waveguide DEMUXes.
Planar lightwave circuits (PLCs) provide various important devices for optical wavelength division multiplexing (WDM), time division multiplexing (TDM) systems, subscriber networks and etc. This paper reviews the recent progress and future prospects of PLC technologies including arrayed-waveguide grating (AWG) wavelength filters, optical add/drop multiplexers (ADM), strictly non-blocking matrix switches, programmable dispersion equalizers and hybrid optoelectronics integration technologies.
In this article, wavelength division multiplexing (WDM) devices suitable for multimode- fiber-based networks are presented. A packaged wavelength division demultiplexer (WDDM) is demonstrated first at wavelengths of 750 nm, 780 nm, 810 nmj and 840 nm. The insersion losses are 8.28 dB, 9.41 dB, 6.78 dB, and 11.71 dB, respectively. The reduction of wavelength separation from 30 nm to 2 nm is achieved using a beveled-edge to couple optical signals into a waveguiding plate. A path-reversed substrate-guided wave holographic interconnection is employed for a WDDM with a channel wavelength spacing as small as 2 nm. A waveguide grating with a 45° incident angle and a 45° diffraction angle is fabricated using 20 pm thick DuPont photopolymer film HRF 600x001. The dispersion and the 3 dB bandwidth of the device are measured to be 0.18°/nm and 20 nm, respectively. A four-channel wavelength demultiplexing is demonstrated at 796 nm, 798 nm, 800 nm, and 802 nm with no crosstalk observed. A one-to-five cascaded 4-channel WDDM with ± 5% energy uniformity under an spolarization is also demonstrated to increase the user-sharing capacity. Twenty fanout channels (5x4) are experimentally achieved. Its potential application for dense WDM at 1555 nm is also addressed. Time-reversal of die demonstrated devices automatically provides the WDM function.
Recent explosive growth of Internet traffic greatly accelerates the needs of telecommunication and networking bandwidth. To satisfy this rapid increase in demand of bandwidth, WDM is the technology of choice. To implement an advanced WDM system, there are needs of various high performance and high complexity photonic devices: multiple wavelength laser arrays, wavelength multiplexer and/or demultiplexer, wavelength router/switches, wavelength add-drop switch, etc. Spectrometer on a chip (SOC) is one of the key enabling technologies to meet those needs. In this paper we review the advancement of planar waveguide WDM technology—from SOC components to integrated SOC WDM systems.
In this paper, we review the previous work in optical code division multiple access (CDMA) systems. Owing to the explosive growth of bandwidth demand in recent years, the current trend in optical communication system designs is to achieve one bit per hertz utilization of the available bandwidth in the optical fiber. Full orthogonality is important in order for optical CDMA systems to achieve high throughput. We describe two spectrally encoded optical CDMA systems which both give us full orthogonality. The throughput of the non-coherent spectral amplitude encoded system is limited by both speckle noise interference and shot noise interference. The multi-wavelength spectral phase encoded system is limited by shot noise only. Performance analysis is also given in this paper.
Ortel recently completed a production run of 4λ WDM OC-48 laser transmitter systems in accordance with a DURIP (Defense University Research Instrumentation Program) contract. The total number of systems manufactured was in excess of 120 (or, 480+ individual laser transmitters), encompassing eight distinct wavelengths. A number of interesting design, manufacturability, and production testing issues were observed. This paper will discuss the details of Oriel's experience which has resulted in a simple, commercially available, low cost OC-48 WDM transmitter system. Finally, a forward looking analysis of new trends in the field of WDM will be presented.
This paper reviews performance of hybrid and monolithically integrated WDM transmitter arrays based on directly modulated 2.5Gbps lasers, with a focus on the wavelength accuracy and stability under normal operating conditions. We also consider power stability, chromatic dispersion penalties, and the channel cross-talk. Large numbers of four-wavelength devices were obtained and evaluated under a program designed to provide university-based system researchers with advanced WDM components We show that multi-wavelength laser arrays capable of high-performance out-of-the-box operation can be now produced for research-type WDM systems.
Future higher-performance systems will be more complex than today's systems since the wavelength domain will be used to help route signals through different static or reconfigurable network paths. In these next-generation systems, several parameters may vary which would have deleterious effects in a WDM environment, including: variable insertion losses, channel addition and deletion (i.e., add/drop multiplexing), unstable laser power, non-uniform EDFA gain, fast gain transients in EDFA cascades, and non-uniform accumulation of dispersion and nonlinearities. In order to ensure robust system operation, we discuss in this paper various dynamic schemes for compensating damaging effects so that these complex systems maintain high performance. Additionally, optical networks will provide high-speed point-to-point connections and passive wavelength routing, but the true power of optics for high-throughput networking will require advances in high-speed optical switching. Significant functions and capabilities can be enabled by high-speed optical switches and cross-connects, but issues regarding control and routing are ripe for extensive research. We highlight one function, that being alloptical packet header replacement.
Optical fiber cable are worldwide installed, e.g. about 43 million kilometers in 1997, an annual growth rate of about 20% is expected. This infrastructure is an excellent basis to convert optical networks based on point-to point systems into managed photonic networks in which new additional photonic equipment is used. Deutsche Telekom started in 1997 some tests with new wavelength division multiplex (WDM) technology in their network in which standard single mode fiber is very dominant. We report on some of these tests and also on first WDM-links in the network carrying real traffic.
The wafer fusion technique for realization of compact waveguide switches, filters and 3D photonic integrated circuits is investigated theoretically and experimentally. Calculations based on the beam propagation method show that very short vertical directional couplers with 40-220 μm coupling lengths and high extinction ratios from 20 to 32 dB can be realized. These extinction ratios can be further improved using a slight asymmetry in waveguide structure. The optical loss at the fused interface was investigated by comparison of the transmission loss in InGaAsP-based ridge-loaded waveguide structures with and without a fused layer near the core region. This reveals an excess loss of 1.1 dB/cm at 1.55 μm wavelength due to the fused interface. Fused straight vertical directional couplers have been fabricated and characterized. Waveguides separated by 0.6 μm gap layer exhibit a coupling length of 62 μm and a switching voltage of about 12 volts. Since GaAs and InP have different material dispersion at 1.55 μm wavelength, a combination of InP and GaAs couplers is used to demonstrate an inherent polarization independent and narrowband filter.
The paper investigates possibilities for high-bit rate transmission systems over embedded standard single-mode fiber (SMF) operating at a transmission wavelength of 1.55 μm. We theoretically analyze 40 Gb/s unrepeated return-to-zero single-channel transmission over 150 km SMF using different dispersion compensation schemes and compare the results to experimental data. It is shown that post-compensation allows for higher fiber-input powers and therefore for a higher system margin. We also numerically compare dispersion-managed 4x40 Gb/s, 16x10 Gb/s and 16x40 Gb/s wavelength-division multiplexed (WDM) transmission over 1000 km standard singlemode fiber operating at 1.55 μm. It is shown, that for Nx40 Gb/s the system performance is mainly limited by the degradation of each individual channel. No significant additional degradation due to cross-phase modulation or four-wave mixing could be observed.