E.S. Kintzer

All-Optical Network Consortium-ultrafast TDM networks

We describe recent results of the Advanced Research Projects Agency (ARPA) sponsored Consortium on Wideband All-Optical Networks which is developing architectures, technology components, and applications for ultrafast 100 Gb/s time-division multiplexing (TDM) optical networks. The shared-media ultrafast networks we envision are appropriate for providing low-access-delay bandwidth on demand to both future high-burst rate (100 Gb/s) users as well aggregates of lower-rate users (i.e., a heterogeneous user population). To realize these goals we are developing ultrafast network architectures such as HLAN, described here, that operate well in high-latency environments and require only limited processing capability at the ultrafast bit rates. We also describe results on 80-Gb/s, 90-km soliton transmission, 100-Gb/s soliton compression laser source technology, picosecond short-pulse fiber ring lasers, picosecond-accuracy optical bit-phase sensing and clock recovery, all-optical injection-locked fiber figure-eight laser clock recovery, short-pulse fiber loop storage, and all-optical pulse width and wavelength conversion.

High‐power strained‐layer InGaAs/AlGaAs tapered traveling wave amplifier

High power, nearly diffraction‐limited cw performance has been obtained from a traveling wave amplifier, fabricated in a strained‐layer InGaAs/AlGaAs laser structure, with a laterally tapered gain region and with a cavity‐spoiling feature to prevent laser oscillation. The input beam diffracts as it propagates, efficiently filling the tapered active region. For input optical power of 85 mW from a Ti:sapphire laser, total cw output of 1.44 W has been achieved with 1.28 W in a central lobe with width less than 1.2 times the diffraction limit at 977 nm wavelength. Only 15 mW of power incident on the amplifier was sufficient to provide 1 W output into the central lobe.

High-power, strained-layer amplifiers and lasers with tapered gain regions

Laterally tapered gain regions designed to accommodate the diffraction of narrow single-lobe beams that have been used in both optical amplifiers and lasers are described. Amplifier output power of 3.5 W with 3.1 W in a 1.05 times diffraction-limited lobe and laser output power of over 4 W with approximately half the power in a 1.7 times diffraction-limited lobe have been achieved.<<ETX>>

Fabrication of two-sided anamorphic microlenses and direct coupling of tapered high-power diode laser to single-mode fiber

An anamorphic microlens has been developed to couple a tapered unstable-resonator laser directly to a single-mode fiber, and has demonstrated capability for simple, compact and efficient high-power diode laser systems. Far high collection and coupling efficiencies, the refractive microlens has been fabricated by utilizing both sides of a GaP substrate, in which the first side was used to remove the astigmatism of the laser output and the second side to focus the beam to a spot size comparable to the fiber mode. The microlenses have been accurately formed by using a recent technique of mass-transport smoothing of etched multimesa preforms. Initial fiber-coupling experiments showed powers as high as 360 mW at the fiber output, and coupling efficiency as high as 29.5% has been measured at a lower power.<<ETX>>

Performance and scalability of an all-optical clock recovery figure eight laser

A novel geometry for all-optical clock recovery using a semiconductor amplifier yields a strong locking mechanism in a short cavity. The recovered clock has a large locking bandwidth, low timing jitter, and fast lock-up time at a 2.5 GHz rate. Preliminary results at a 9 GHz rate also indicate a high quality recovered clock.

High-data-rate systems for space applications

High data rate communications systems will soon be needed for space applications. Technology and applications which support high data rates are already in place for ground- based telecommunications, or will be in the future. The advantages of an optical system over a traditional RF link for free space communications are particularly compelling for high data rates. We have been developing the necessary technology to demonstrate the feasibility of high rate free-space optical communications technology at 1.5 micrometers . The existence of a large, mature technology base at 1.5 micrometers developed for the telecommunications industry has allowed us to focus our development effort on two key technologies needed for space applications that have not been developed for the ground: a 1 Watt class optical power amplifier and a near quantum limited receiver. This paper will describe the overall system design for a high data rate optical communications system and present experimental results demonstrating < 50 photons/bit sensitivity at 10 Gbps with 1 Watt of optical power. The existence of a feasibility demonstration at this data rate enables downward scalability to data rates of 1 Gbps or less with small, inexpensive terminals.

Single-mode optical fiber coupling of high-power tapered gain region devices

A simple method for collimating the optical output of a tapered gain region amplifier or laser and coupling to a single-mode optical fiber is described, along with a technique for quantitatively assessing the expected coupling efficiency. By using a tapered laser, 840 mW at 980 mm was coupled into single-mode fiber with 44% efficiency measured from fiber input to available internal fiber power, in excellent agreement with the 48% predicted. When transmission losses of the collimating optics are included, the power coupling efficiency referred to the laser facet power is 32%.<<ETX>>

A one-watt, 10-Gbps high-sensitivity optical communication system

High data rate communications are of interest for many applications. In fiber-based broadcast systems, high receiver sensitivity and high transmitter power translate into the ability to reach more customers. For space applications, high receiver sensitivity and high optical power are essential since it is impossible to use amplifiers between the transmitter and receiver. We describe here the experimental demonstration of a 10-Gbps communications system with a receiver sensitivity of 77 photons/bit at a bit error rate of 10/sup -9/ and a one-watt optical transmitter based on an erbium-doped fiber amplifier pumped by tapered-gain-region semiconductor lasers.<<ETX>>

Single-spatial-mode tapered amplifiers and oscillators

The recent development of semiconductor diode optical amplifiers and lasers having a laterally tapered gain region has changed the outlook for high-power semiconductor optical sources. For the first time, highbrightness, single-element, all-semiconductor sources which emit several watts of cw power in a nearly ideal, single-lobed, diffraction-limited beam have been demonstrated. As semiconductor sources these devices have the inherent advantages of high efficiency, small size, light weight, and reliability. The amplifier12 and all-semiconductor master-oscillator power-amplifier (MOPA) devices34 have gain regions linearly tapered from a few micrometers at the amplifier input to several hundred micrometers at the output. Device lengths are typically 2 mm or more. The angle of the taper is chosen to match the diffraction angle of the input beam which has its waist near the narrow end of the taper. Such a structure is shown schematically in Fig. 1 . The etched grooves have angled side walls and act as cavity spoilers, designed to prevent oscillation of the device as a broad-area laser. The devices are fabricated in single-quantum-well strained-layer InGaAs/AlGaAs graded-index separate-confinement heterostructure laser wafers grown by organometallic vapor phase epitaxy.5 The tapered devices also operate as laser oscillators6 by increasing the input facet reflectivity. For amplifiers, both the input and output facets are coated for low reflectivity (in Fig. 1 , Ri = R2 = 1%), but for oscillators, the input facet is left uncoated (R1 —30%). The oscillators also emit several watts of cw power into a nearly single-lobed, nearly diffraction-limited beam, though their beam quality is usually somewhat inferior to that obtained for amplifiers, particularly at the highest output powers. The lateral mode of the oscillator is similar to the modes described by Fox and Li7 for unstable resonators, except that the semiconductor medium has a significant effect on the self-consistent mode which oscillates. A beam propagation calculation has been carried out to model these effects, as described below. This paper includes a review of the properties of both tapered amplifiers and oscillators.

Gbps-class optical communications systems for free-space applications

For very high data rates, optical communications holds a potential performance edge over other technologies, especially for space applications where size, weight, and power are of prime importance. We report demonstrations of several Gigabit-per-second (Gbps) class all- semiconductor optical communications systems which have been developed for free-space satellite crosslink applications. These systems are based on the master-oscillator-power- amplifier (MOPA) transmitter architecture which resolves the conflicting requirements of high speed and high power on a single-laser coherent transmitter. A 1 Gbps, 1 Watt system operating at 973 nm with a frequency-shift-keyed (FSK) modulation format is the highest power coherent optical communications system using all semiconductor lasers reported to date. A 3 Gbps differential-phase-shift-keyed (DPSK) system uses a 2-stage injection-locked diode array as a power amplifier at 830 nm. At a wavelength of 1.5 micrometers , an optically- preamplified direct-detection on-off-keyed (OOK) receiver was demonstrated at both 3 and 10 Gbps. A 3 Gbps optically-preamplified direct-detection DPSK receiver was also demonstrated and represents, to our knowledge, the highest sensitivity DPSK receiver reported to date for data rates above 2 Gbps.