This paper describes integrated optics modulators which meet the requirements introduced by hybrid fiber coax system architectures, and the design criteria and performance data for both the devices and externally modulated systems. Advantages associated with external modulators include high power operation, chirpless operation at 1550 nm, compatibility with optical amplifiers, optimal performance for the distribution of analog signals to optical distribution nodes from head ends/central offices, integral means for SBS suppression, flat frequency and phase response to 1 GHz, high impedance (50 ohm) operation, and stable operating characteristics over a range of environmental conditions.
A technique, based on quantum well (QW) intermixing, has been developed for the post growth, spatially selective tuning of the QW bandgap in a laser structure. High energy (MeV) ion implantation is used to create a large number of vacancies and interstitials in the device. During high temperature processing, these defects simultaneously enhance the intermixing of the QW and the barrier materials, producing a blue shift of the QW bandgap, and are annealed out. Increases in bandgap energy (measured using low temperature photoluminescence spectroscopy) of greater than 60 meV can be achieved. Absorption spectroscopy in the waveguide direction is also used to quantify any excess loss in the structure. Using a simple masking scheme to spatially modify the defect concentration, different regions of a wafer can be blue shifted by different amounts. This allows the integration of many different devices such as lasers, detectors, modulators, waveguides etc. on a single wafer using only a single, post-growth processing step. The performance of both passive (waveguide) and active (laser) devices produced using this technique is described, as well as the practicality of this technique in the production of photonic integrated circuits.
Recent progress in rare earth doped LiNbO3 integrated optic lasers and optical amplifiers is first reviewed. We report the results of an alternative pumping scheme and co-dopants for Er:LiNbO3 guided wave optical amplifiers.
Characteristics of strained-layer InGaAs/GaAs/AlGaAs lasers with monolithically integrated photodiodes fabricated by selective-area epitaxy are presented. Threshold currents as low as 8 mA (approximately 300 A/cm2) were obtained for uncoated devices operating cw at room temperature. Responsivities of 71, 41, and 6.7 (mu) A/mW was obtained for devices with photodiode etched facet angles of 3 degree(s), 14 degree(s), and 45 degree(s), respectively, and a photodiode bias of 0 V.
This paper reviews the state-of-the-art of monolithic integration of InP grating-based WDM components. We will discuss the two basic types of InP integrated wavelength demultiplexers: the etched reflection grating spectrograph and the phased-array demultiplexer. They will be compared in terms of their performance and ease of fabrication. Current trends and examples of integration with active components will be presented. In addition, the crucial issue of the wavelength precision of these devices will be addressed.
We describe distributed Bragg pulse shapers for the ultra-fast communication system wavepacket encoding. We discuss Bragg pulse shaper design and fabrication and we present experimental results from first and second generation devices.
We report on manufacturable, low cost scheme for precision packaging a monolithically integrated GaAs optical receiver. Silicon V-groove and flip-chip bonding technologies are used to reliably achieve the required alignment accuracy. A silicon fiber carrier, which houses the fiber in a V-groove, is flip-chip bonded on to the receiver chip. The light from the cleaved end of the fiber is reflected off the V-groove end on to the planar photodetector, with an optical coupling efficiency of 85%. The entire fiber attach process uses standard semiconductor fabrication and processing techniques, making it attractive for low cost manufacturing.
In this paper we will review our efforts in developing both design and fabrication capabilities for photonic integrated circuits. Design is based on software for CAD and beam propagation simulation of planar waveguide circuits. Fabrication is based on a laser-based rapid prototyping system for patterning and processing waveguide materials.
The ability to efficiently connect many high-speed parts is of critical importance for large- capacity data communications. High bandwidth, 2D optical planes can be employed to achieve such an interconnection and avoid electronic bottlenecks. A novel solution which dramatically increases the functionality of optical-plane interconnections uses wavelength multiplexing to facilitate one 2D optical plane interconnecting reconfigurably with many other planes. We report the first experimental demonstration of using wavelength multiplexing to facilitate reconfigurable interconnections between one pixel on the source plane and one pixel on each of several detector planes. We show the near-error-free 155 Mb/s transmission and detection of 3 different wavelengths at three detector planes.
Long wavelength optoelectronic integrated circuits (OEICs) have made impressive progress in the last decade and their performance has become attractive enough to be considered as part of lightwave communication systems. This paper reviews these aspects of OEICs, with emphasis on monolithic photoreceivers which incorporate heterojunction bipolar transistors for the electronic functions. We review single channel p-i-n/HBT photoreceivers with speeds up to 12 Gb/s and multi-channel array-type receivers suitable for WDM applications with an aggregate throughput of 20 Gb/s.
The rapid emergence of high-performance optical systems has accentuated the need for photodiodes with enhanced performance and functionality. In this paper we will describe a new class of photodiodes that utilize novel resonant-cavity structures to achieve high speed, high quantum efficiency, and a narrow spectral response which may prove useful for some wavelength division multiplexing applications. The resonant-cavity photodiode consists of a thin absorbing layer sandwiched between two dielectric mirrors. One advantage of this structure is that it can be utilized to circumvent the responsivity/bandwidth tradeoff inherent to conventional PIN photodiodes structures. For the typical normal-incidence photodiode a wide bandwidth necessitates a thin absorption layer which, in turn, results in low quantum efficiency. The resonant-cavity structure, on the other hand, effectively decouples the responsivity from the transit-time component of the bandwidth because the optical signal makes multiple passes across the thin absorbing layer inside the microcavity. The resonant- cavity approach has been utilized for p-i-n photodiodes, phototransistors, dual-wavelength photodetectors, avalanche photodiodes (APDs), and Schottky barrier photodiodes. In this paper we will concentrate on two specific devices, a Si1-x/Gex resonant-cavity p-i-n photodiode and a resonant-cavity APD with separate absorption and multiplication regions.
A research program at The MITRE Corporation was developed to examine all-optical networks. The central element in this all-optical local area network research testbed was an optical crossbar switch employing semiconductor optical amplifiers (SOAs) as the switching and gain elements. One of the initial applications demonstrated on this all-optical testbed was the capability to transmit amplitude modulated (AM) analog signals through this network. The successful implementation of this capability demonstrates that analog imagery, telemetry, radio frequency communications, and sensor information can be distributed over a switched all-optical network. The principal challenge associated with the transmission of AM signals through the all-optical network are the limitations imposed by the SOAs in the switch. These devices exhibit non-linear transfer characteristics, have limited dynamic range, and high noise levels. This paper will describe the techniques developed to demonstrate acceptable video signal transmission performance through the all-optical switched testbed using FM modulation and microwave subcarrier technology.
We present a novel all fiber device for use as a high speed optical demultiplexer and logic gate. The device has particular applicability to demultiplexing for high data rate optical networks in addition to all optical address recognition via XOR gating.
The optimized power performance and the spectral tunability modeling of Erbium-doped fiber ring lasers are presented together with the measurement of the relative intensity noise. A Figure of Merit and an optimization procedure are defined in order to obtain maximum output power for a given pump power aiming the project design. Two tunable Erbium-doped fiber ring lasers were assembled. Their tunabilities are modeled and compared to the experimental results. Good agreement was obtained. We achieved a 32 nm tuning range, limited by the tuning range of the filter used. A relative intensity noise < - 120 dB/Hz, which enables to externally modulate such lasers up to 2.5 Gb/s, was also obtained.
The equations describing the stimulated Brillouin scattering process in optical fibers with distributed gain, including an equation for the second-order Stokes wave, are numerically solved. An analytical solution for the case of no net gain or loss is also presented. We note that the presence of distributed gain along the fiber leads to a non-monotonous evolution of the signal power and to ready generation of multiple Stokes orders. The influence of a copropagating or counterpropagating signal at the first or second-order Stokes wavelength, respectively, is also examined.
The authors have developed a method that can control the active mode-locked fiber ring laser at three different repetition rate. Driven by 2.5 GHz microwave signal the active mode-locked fiber ring laser can generate 2.5 GHz, 5 GHz and 7.5 GHz optical pulses by tuning the bias voltage and microwave power. The product of pulse width and spectrum width was near 0.315.
Ti-Au and annealed Ti-Pt-Au p-type contacts are demonstrated to improve the adhesion over a pure gold contact and allow annealing of the metallization to thin p-cladding laser structures at the expense of an increase in the optical loss. As little as 10 angstroms of titanium is adequate for an adhesion layer and only increases the optical loss by 1.6 cm-1 over a pure gold metallization which has an optical loss of 10.0 cm-1. A metallization of 15 angstroms Ti - 15 angstroms Pt - 1500 angstroms Au is adequate for an anneal at 410 degree(s)C for 10 sec and increases the optical loss by 7.0 cm-1.