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

We present a theoretical study of the effect of radiation losses on the mode selectivity of DFB lasers with second-order gratings. For a second-order grating, interference of the radiation due to first-order diffraction of oppositely propagating guided waves cancels the radiation loss at one of the edges of the spectrum gap. This provides threshold gain discrimination of order 10 cm-1against one of the two dominant modes occurring near the edges of the gap. This should allow fabrication of DFB lasers with properties that are nearly independent of the positions of the facets relative to the grating corrugations, which are uncontrolled. By applying antireflection coatings to the two ends, differential quantum efficiencies close to those of conventional Fabry-Perot lasers should be achievable.

Second-order distributed feedback lasers with mode selection provided by first-order radiation losses

A single longitudinal mode (SLM) operating condition for phase-adjusted (PA) DFB lasers has been made clear both experimentally and theoretically. As expected, we got a high SLM operation yield of 80 percent in a moderate coupled case up to a light output power of 10 mW. However, in the strongly coupled cases, the two-mode operation with the TE0 mode and the TE + 1 mode occurred frequently. To explain the two-mode operation and to optimize the PA-DFB laser structure, we have developed a theory. Taking the spatial hole burning along the laser axis into account, we succeeded in explaining the longitudinal mode behavior. From our theory, moderate coupling ( kL = 1.25 ) was found to be optimum to maintain the large threshold gain difference above threshold.

Stability in single longitudinal mode operation in GaInAsP/InP phase-adjusted DFB lasers

For high-bit-rate long-haul fiber optic communications, the avalanche photodiode (APD) is frequently the photodetector of choice owing to its internal gain, which provides a sensitivity margin relative to PIN photodiodes. APDs can achieve 5-10-dB better sensitivity than PINs, provided that the multiplication noise is low and the gain-bandwidth product is sufficiently high. In the past decade, the performance of APDs for optical fiber communication systems has improved as a result of improvements in materials and the development of advanced device structures. This paper presents a brief review of APD fundamentals and describes some of the significant advances

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Recent Advances in Telecommunications Avalanche Photodiodes

High-speed modulation and 4.4 fJ bit−1 data transmission is demonstrated using a photonic-crystal nanocavity laser. Its current threshold of 4.8 µA, modulation current efficiency of 2.0 GHz µA−0.5 and output power of 2.17 µW may enable on-chip photonic networks in combination with recently developed high-sensitivity receivers.

Few-fJ/bit data transmissions using directly modulated lambda-scale embedded active region photonic-crystal lasers

Room temperature CW operation of distributed-feedback buried-heterostructure InGaAsP/InP lasers emitting at 1.57 μm was achieved. A DC threshold of about 250 mA at 25°C and a temperature coefficient of the lasing wavelength of 1.0 A/°C were obtained. Some of these lasers manifested single longitudinal mode operation both in DC condition and in deeply modulated condition at 500 Mbit/s.

Room-temperature cw operation of distributed-feedback buried-heterostructure ingaasp/inp lasers emitting at 1.57 μm

The optical response time of an InGaAs/InP heterostructure avalanche photodiode (HAPD) with InGaAsP buffer layers is reported. It is shown that the buffer layers play an important role in reduction of the pile-up effect and are considered to be effective in achieving high-speed InGaAs/InP HAPDs.

High-speed-response InGaAs/InP heterostructure avalanche photodiode with InGaAsP buffer layers

Room-temperature c.w. operation of InGaAsP/InP heterostructure lasers grown by liquid-phase epitaxy was achieved at 1.56 μm. An active InGaAsP layer was essentially sandwiched by InP, though a thin InGaAsP buffer layer was deposited to prevent the melt-back of the active layer. Threshold current was typically 300 mA for a 17 μm wide oxide-defined stripe laser.

Room temperature c.w. operation of InGaAsP/InP heterostructure lasers emitting at 1.56 μm

10 Gbit/s optical demultiplexing and switching were performed by sinusoidally driven InGaAsP electroabsorption modulators, for the first time. An optical gate with variable gate width was obtained just with sinusoidal voltage. In-line demultiplexing/switching by the modulator was effective in reducing the amplified spontaneous emission noise in optical amplifier systems.

10 Gbit/s optical demultiplexing and switching by sinusoidally driven InGaAsP electroabsorption modulators

InGaAsP/InP buffer-layer loaded planoconvex waveguide lasers are reported. The CW threshold current at 20°C was 70 mA. The maximum CW operating temperature of 70°C was achieved. The characteristic temperature under CW operation was 51 K. Operation in fundamental transverse mode and single longitudinal mode up to 1.9 and 1.4 times the threshold current, respectively, was obtained.

Yuichi Matsushima

Papers

Room-temperature cw operation of distributed-feedback buried-heterostructure ingaasp/inp lasers emitting at 1.57 μm

High-speed-response InGaAs/InP heterostructure avalanche photodiode with InGaAsP buffer layers

Room temperature c.w. operation of InGaAsP/InP heterostructure lasers emitting at 1.56 μm

10 Gbit/s optical demultiplexing and switching by sinusoidally driven InGaAsP electroabsorption modulators

High temperature CW operation of 1.5 μm InGaAsP/InP buffer-layer loaded planoconvex waveguide lasers