All-optical label swapping is a promising approach to ultra-high packet-rate routing and forwarding directly in the optical layer. In this paper, we review results of the DARPA Next Generation Internet program in all-optical label swapping at University of California at Santa Barbara (UCSB). We describe the overall network approach to encapsulate packets with optical labels and process forwarding and routing functions independent of packer bit rate and format. Various approaches to label coding using serial and subcarrier multiplexing addressing and the associated techniques for label erasure and rewriting, packet regeneration and packet-rate wavelength conversion are reviewed. These functions have been implemented using both fiber and semiconductor-based technologies and the ongoing effort at UCSB to integrate these functions is reported. We described experimental results for various components and label swapping functions and demonstration of 40 Gb/s optical label swapping. The advantages and disadvantages of using the various coding techniques and implementation technologies are discussed.

All-optical label swapping networks and technologies

The main bandwidth bottleneck in today's networks is in the access segment. To address that bottleneck, broadband fiber access technologies such as passive optical networks (PONs) are an indispensable solution. The industry has selected time-division multiplexing (TDM) for current PON deployments. To satisfy future bandwidth demands, however, next-generation PON systems are being investigated to provide even higher performance. In this paper, we first review current TDM-PONs; we designate them as generation C. Next, we review next-generation PON systems, which we categorize into C+1 and C+2 generations. We expect C+1 systems to provide economic near-term bandwidth upgrade by overlaying new services on current TDM-PONs. For the long term, C+2 systems will provide more dramatic system improvement using wavelength division multiplexing technologies. Some C+2 architectures require new infrastructures and/or equipment, whereas others employ a more evolutionary approach. We also review key enabling components and technologies for C+1 and C+2 generations and point out important topics for future research.

/pdf/next-generation-optical-access-networks-41pmztcn8d.pdf

Next-Generation Optical Access Networks

Tunable semiconductor lasers have been listed in numerous critical technology lists for future optical communication and sensing systems. This paper summarizes a tutorial that was given at OFC '03. It includes some discussion of why tunable lasers might be beneficial, an outline of basic tuning mechanisms, some examples of tunable lasers that have been commercialized, and a discussion of control techniques. More extensive data is given for the widely-tunable sampled-grating distributed-Bragg-reflector (SGDBR) type of laser, including data for such lasers integrated monolithically with modulators to form complete transmitter front ends. A summary of reliability data for the SGDBR laser is also given. It is concluded that tunable lasers can reduce operational costs, that full-band tunability is desirable for many applications, that monolithic integration offers the most potential for reducing size, weight, power and cost, and that sufficient reliability for system insertion has been demonstrated.

/pdf/tunable-semiconductor-lasers-a-tutorial-u60opvuxtv.pdf

Tunable semiconductor lasers: a tutorial

After over two decades of exploration, tunable diode lasers are beginning to find significant applications, driven largely by the huge demand for bandwidth that is guiding many developments in the optical fiber communication business today. In the paper, some of the history and key developments that have led to the technologies available today are reviewed from the perspective of the author. After discussion of some of the early work, the focus shifts to widely tunable diode lasers, which would appear to be key enablers for future dense wavelength-division multiplexing and optical switching and networking systems. The distinguishing characteristics of the current technological alternatives are summarized.

Monolithic tunable diode lasers

Vertical-cavity surface-emitting lasers (VCSELs) are now key optical sources in optical communications. Their main application is currently in local area networks using multimode optical fibers. VCSELs are also being rapidly commercialized for single-mode fiber metropolitan area and wide area network applications. The advantages of VCSEL include simpler fiber coupling, easier packaging and testing, and the ability to be fabricated in arrays. In addition, VCSELs have an inherent single-wavelength structure that is well suited for wavelength engineering. All these advantages promise to lead to cost-effective wavelength-tunable lasers, which are essential for the future intelligent, all-optical networks. The author reviews the advances on wavelength-tunable VCSELs. She summarizes some of the early breakthroughs in wavelength engineering of VCSELs and then concentrates on the designs and properties of micromechanical tunable VCSEL.

Tunable VCSEL

A vertical-grating-assisted codirectional coupler laser with rear sampled grating reflector (GCSR laser) combines single-mode operation over a very wide tuning range of 74 nm with a side-mode suppression of better than 30 dB over most of the wavelength span. The total tuning span is limited by the combined bandwidths of the active material gain curve and the envelope of the sampled grating reflection peak spectrum, while the tuning capacity of the directional coupler filter alone is estimated to be at least 140 nm. >

74 nm wavelength tuning range of an InGaAsP/InP vertical grating assisted codirectional coupler laser with rear sampled grating reflector

We report improved tuning regularity in a vertical grating assisted codirectional coupler laser with a super-structure grating distributed Bragg reflector (GCSR). Access to 20 wavelengths with SMSR better than 20 dB within a tuning range of 100 nn was obtained with a single current control in a GCSR laser. The total tuning behavior shows a potential of complete wavelength coverage over 100 nm by use of three tuning currents. >

Access to 20 evenly distributed wavelengths over 100 nm using only a single current tuning in a four-electrode monolithic semiconductor laser

A continuous wavelength tuning range of 5.4 nm is obtained for a three-section DBR (distributed Bragg reflector) laser by applying one control current in both forward and reverse bias directions. In the reverse direction no significant linewidth broadening is seen due to the absence of injection-recombination shot noise, and a linewidth of less than 3 MHz is obtained over a wavelength span of 1.8 nm. The minimum linewidth observed is 580 kHZ. >

Wide continuous wavelength tuning of a narrow linewidth DBR laser

A small signal amplitude modulation bandwidth of 20 GHz has been obtained with a three-section tunable DBR laser fabricated with semi-insulating current blocking layers grown by hydride VPE. The modulation bandwidth and laser linewidth are strongly dependent on the position of the lasing mode relative to the Bragg reflection peak. >

Increased modulation bandwidth up to 20 GHz of a detuned-loaded DBR laser

popula, ginkgo, and zelkova were used for measurement. They were collected at our university just before measurement and kept them alive by holding them with water pad during measurement. Examples of LIF spectra of zelkova leaf are shown in Figs. 1 and 2. The intensities are normalized by that at 685 nm, which is one component of chlorophyll described later. In general, they showed four characteristic broad-band spectra at around 450 run, 550 nm, 685 nm, and 740 nm. The former two spectra were derived from some plant pigments' like NADPH, trans-p-carotene, vitamin K, and riboflavin, and the latter ones from chlorophyll A whose shape indicated existence of two molecular species. As each of them was not separated into its origin experimentally, development of software using non-linear curve fitting techniques is in progress to make clear the origins of each peaks. Dominant peaks of LIF spectra appeared at around 685 nm and 740 nm in summer when the leaf color was dark green and photosynthesis process were very active. On the contrary, in winter the configuration of LIF spectra entirely changed. Effects of other pigments except chlorophyll became much larger on LIF spectra and the peak at 740 nm disappeared. These phenomena were observed due to reducing self-absorption of fluorescence around 685 nm with fading chlorophyll pigments with senescence of leaves? Partial difference of LIF spectra with coloring is shown in Fig. 2 corresponding to real colors. It shows clearly the effect of pigments in the leaf on the LIF spectra. It was shown that LIF spectra of intact leaves contained much information about status of plant growth. They will be useful to develop a fluorescence lidar for vegetation monitoring to diagnose remotely health status of plants like stress, damage, senescence, death, and so on. 1. E. W. Chappelle, et a/., Appl. Opt. 23, 134 (1984). 2. K. Takahashi, et al., in Proc. IGARSS '93, 1985-1987 (1993). Tunable semiconductor lasers and their applications

L. Backbom

Papers

74 nm wavelength tuning range of an InGaAsP/InP vertical grating assisted codirectional coupler laser with rear sampled grating reflector

Access to 20 evenly distributed wavelengths over 100 nm using only a single current tuning in a four-electrode monolithic semiconductor laser

Wide continuous wavelength tuning of a narrow linewidth DBR laser

Increased modulation bandwidth up to 20 GHz of a detuned-loaded DBR laser

Tunable semiconductor lasers and their applications