WDM networks make a very effective utilization of the fiber bandwidth and offer flexible interconnections based on wavelength routing. In high capacity, dynamic WDM networks, blocking due to wavelength contention can he reduced by wavelength conversion. Wavelength conversion addresses a number of key issues in WDM networks including transparency, interoperability, and network capacity. Strictly transparent networks offer seamless interconnections with full reconfigurability and interoperability. Wavelength conversion may be the first obstacle in realizing a transparent WDM network. Among numerous wavelength conversion techniques reported to date, only a few techniques offer strict transparency. Optoelectronic conversion (O/E-E/O) techniques achieve limited transparency, yet their mature technologies allow deployment in the near future. The majority of all-optical wavelength conversion techniques also offer limited transparency but they have a potential advantage over the optoelectronic counterpart in realizing lower packaging costs and crosstalk when multiple wavelength array configurations are considered. Wavelength conversion by difference-frequency generation offers a full range of transparency while adding no excess noise to the signal. Recent experiments showed promising results including a spectral inversion and a 90 nm conversion bandwidth. This paper reviews various wavelength conversion techniques, discusses the advantages and shortcomings of each technique, and addresses their implications for transparent networks.

Wavelength conversion technologies for WDM network applications

We report demonstration of a new high-power semiconductor laser technology, the optically pumped semiconductor (OPS) vertical-external-cavity surface-emitting laser (VECSEL). Using diode laser pump, an OPS-VECSEL laser with a strain-compensated InGaAs-GaAsP-GaAs multiquantum-well (MQW) structure operated continuous-wave (CW) near /spl lambda//spl sim/1004 nm with record output power of 0.69 W in a TEM/sub 11/ mode, 0.52 W in a TEM/sub 00/ mode, and 0.37 W coupled to a single-mode fiber. It is feasible to produce greater than 1 W of power in a diffraction-limited circular beam from an efficient, compact, manufacturable and reliable OPS-VECSEL laser.

High-power (>0.5-W CW) diode-pumped vertical-external-cavity surface-emitting semiconductor lasers with circular TEM/sub 00/ beams

We describe the design, fabrication, and measured characteristics of the high-power optically pumped-semiconductor (OPS) vertical-external-cavity surface-emitting lasers (VCSELs). Using diode laser pumping, we have recently demonstrated operation of such lasers, which for the first time generate high (watt-level) power and a circular Gaussian beam directly from a semiconductor laser. These OPS-VECSELs have a strain-compensated multi-quantum-well InGaAs-GaAsP-GaAs structure and operate CW near /spl lambda//spl sim/1004 nm with output power of 0.69 W in TEM/sub 11/ mode, 0.52 W in TEM/sub 00/ mode and 0.37 W coupled to a single-mode fiber. With multiple pump and gain elements, OPS-VCSEL technology is scalable to the multiwatt power levels. Such lasers will prove useful in a variety of applications requiring compact and efficient sources with high-power output in a single-mode fiber or with diffraction-limited beam quality.

Design and characteristics of high-power (>0.5-W CW) diode-pumped vertical-external-cavity surface-emitting semiconductor lasers with circular TEM/sub 00/ beams

The technical core of a precompetitive consortium formed by AT&T, DEC, and MIT to study the technology, architecture and applications of wideband all-optical networks of local to national (or international) extent is described. A general introduction to all-optical networks is given, and some proposed applications are discussed. The architecture, technology and testbed portions of this effort are described. >

A precompetitive consortium on wide-band all-optical networks

Surface-emitting semiconductor lasers can make use of external cavities and optical pumping techniques to achieve a combination of high continuous-wave output power and near-diffraction-limited beam quality that is not matched by any other type of semiconductor source. The ready access to the laser mode that the external cavity provides has been exploited for applications such as intra-cavity frequency doubling and passive mode-locking. The purpose of this Topical Review is to outline the operating principles of these versatile lasers and summarize the capabilities of devices that have been demonstrated so far. Particular attention is paid to the generation of near-transform-limited sub-picosecond pulses in passively mode-locked surface-emitting lasers, which are potentially of interest as compact sources of ultrashort pulses at high average power that can be operated readily at repetition rates of many gigahertz.

https://eprints.soton.ac.uk/15016/1/TropperJPD04.pdf

Vertical-external-cavity semiconductor lasers

The use of disk geometry, optically pumped semiconductor gain elements for high‐power scalability and good transverse mode quality has been studied. A room‐temperature TEM00 transverse mode, external‐cavity GaAs disk laser has been demonstrated with 500 W peak‐power output and 40% slope efficiency, when pumped by a Ti:Al2O3 laser. The conditions for diode laser pumping are shown to be consistent with available power level.

Scalable high‐power optically pumped GaAs laser

Optically pumped InGaAs/GaAs/AlGaAs heterostructure lasers exhibit differential quantum efficiencies that are not sensitive to output coupling or active length, indicating low free carrier absorption loss. A broad‐stripe 2.5‐mm‐long device yielded 4‐W average power and 20‐W peak power.

Diode‐laser‐pumped InGaAs/GaAs/AlGaAs heterostructure lasers with low internal loss and 4‐W average power

The ultrafast, room-temperature, resonance-enhanced third-order nonlinear susceptibility tensor of an AlGaAs/GaAs quantum well is determined. A single 6-nm GaAs quantum well embedded in a waveguide of 382-nm mode size increases the |χ(3)| from a bulk-material level of 8 × 10−11 esu ±20% to 6 × 10−10 esu ±20%. The anisotropy of the diagonal elements ∣χ1111(3)∣,∣χ2222(3)∣ and their correlation with the off-diagonal elements ∣χ1212(3)∣,∣χ2121(3)∣ are consistent with the one-photon resonance mechanism.

Ultrafast, room-temperature, resonance-enhanced third-order optical susceptibility tensor of an AlGaAs/GaAs quantum well.

Optical nonlinearties of AlxGa1−xAs/GaAs asymmetric coupled quantum wells within a p-i-n structure have been observed by using time-resolved spectroscopy. Under photoexcitation, exciton absorption lines exhibit spectral shifts of as much as ≈1 meV. The recovery times of these spectral shifts are of the order of hundreds of picoseconds when the excitation photon is above the lowest exciton state but become less than 10 psec when excitation is below the lowest exciton state, indicating a virtual process. The behavior of these spectral shifts is consistent with the presence of a polarization induced by optical pumping. The polarization is believed to be due to the excitons that have nonvanishing electric dipole moments along the axis of the asymmetric coupled quantum wells.

Optical nonlinearities in Al(x)Ga(1-x)As/GaAs asymmetric coupled quantum wells.

Nondegenerate four-wave mixing in a single-mode ridge waveguide has been demonstrated as a technique for simultaneous measurement of the imaginary component and the absolute magnitude of the third-order nonlinear susceptibility χ(3). In the same experimenal apparatus, Im χ(3)(ω2 = ω1 + ω2 − ω1) was obtained by measuring the pump-induced probe power loss and |χ(3)(ω3 = ω1 + ω1 − ω2)| was derived from Stokes wave generation efficiency. The ratio of these quantities was obtained without significant system uncertainties. The technique has been applied to AlGaAs/GaAs quantum-well waveguides with picosecond laser pulses. For ħω1 ≈ ħω2 ≈ 1.43 eV, it was found that Im χ(3) = (6.1 ± 0.5) × 10−11 esu, |χ(3)| = (7.6 ± 1.7) × 10−11 esu with a system uncertainty of 25%, and Im χ(3)/|χ(3)| = 0.8 ± 31%, indicating the dominance of two-photon absorption.

H. Q. Le

Papers

Scalable high‐power optically pumped GaAs laser

Diode‐laser‐pumped InGaAs/GaAs/AlGaAs heterostructure lasers with low internal loss and 4‐W average power

Ultrafast, room-temperature, resonance-enhanced third-order optical susceptibility tensor of an AlGaAs/GaAs quantum well.

Optical nonlinearities in Al(x)Ga(1-x)As/GaAs asymmetric coupled quantum wells.

Measurement of third-order optical nonlinear susceptibility using four-wave mixing in a single-mode ridge waveguide.