Avalanche Photodiodes (APDs) are widely used in fiber-optic communications as well as imaging and sensing
applications where high sensitivities are needed. Traditional InP-based APD receivers typically offer a 10 dB
improvement in sensitivity up to 10 Gb/s when compared to standard p-i-n based detector counterparts. As the data rates
increase, however, a limited gain-bandwidth product (~100GHz) results in degraded receiver sensitivity. An increasing
amount of research is now focusing on alternative multiplication materials for APDs to overcome this limitation, and one
of the most promising is silicon. The difficulty in realizing a silicon-based APD device at near infrared wavelengths is
that a compatible absorbing material is difficult to find. Research on germanium-on-silicon p-i-n detectors has shown
acceptable responsivity at wavelengths as long as 1550 nm, and this work extends the approach to the more complicated
APD structure. We are reporting here a germanium-on-silicon Separate Absorption Charge and Multiplication (SACM)
APD which operates at 1310 nm, with a responsivity of 0.55A/W at unity gain with long dark current densities. The
measured gain bandwidth product of this device is much higher than that of a typical III-V APD. Other device
performances, like reliability, sensitivity and thermal stability, will also be discussed in this talk. This basic
demonstration of a new silicon photonic device is an important step towards practical APD devices operating at 40 Gb/s,
as well as for new applications which require low cost, high volume receivers with high sensitivity such as imaging and
sensing.
This paper presents the first scribing results obtained by combining a short-pulse 10ns green laser with the water jet-guided
laser technology. A number of high-potential applications are presented, from the grooving of low-k silicon
wafers, the scribing of metallic and amorphous Si layers of thin film solar cells, the grooving of SiC wafers, and dot
marking of Si wafers. The combination of a short pulse laser beam with the water jet-guided laser technology offers a
new industry-proven alternative for grooving and scribing processes, providing superior speed and quality compared to
legacy laser technologies.
Single photon detection at telecom wavelengths is of importance in many industrial applications ranging from quantum
cryptography, quantum optics, optical time domain reflectometry, non-invasive testing of VLSI circuits, eye-safe
LIDAR to laser ranging. In practical applications, the combination of an InGaAs/InP APD with an appropriate
electronic circuit still stands as the best solution in comparison with emerging technologies such as superconducting
single photon detectors, MCP-PMTs for the near IR or up-conversion technique.
An ASIC dedicated to the operation of InGaAs/InP APDs in both gated mode and free-running mode is presented. The
1.6mm2 chip is fabricated in a CMOS technology. It combines a gate generator, a voltage limiter, a fast comparator, a
precise timing circuit for the gate signal processing and an output stage. A pulse amplitude of up to +7V can be
achieved, which allows the operation of commercially available APDs at a single photon detection probability larger
than 25% at 1.55&mgr;m. The avalanche quenching process is extremely fast, thus reducing the afterpulsing effects. The
packaging of the diode in close proximity with the quenching circuit enables high speed gating at frequencies larger
than 10MHz. The reduced connection lengths combined with impedance adaptation technique provide excellent gate
quality, free of oscillations or bumps. The excess bias voltage is thus constant over the gate width leading to a stable
single photon detection probability and timing resolution. The CMOS integration guarantees long-term stability,
reliability and compactness.
A compact single photon detector designed for the detection in the visible spectral range is presented. A fast active quenching circuit is integrated on the chip in order to operate the APD in single photon counting mode. The sensor consists of a 0.8x0.8mm2 silicon chip mounted on a thermo-electric cooler and packaged in a standard TO5 header, bringing the degree of miniaturization to a level never reached. Reliability, compactness, low power and low cost make the detector essential for portable devices, implantable sensors, fluorescence lifetime spectrometers or laser scanning microscopes. In addition, the sensor exhibits best-in-class timing resolution of 50ps. The photon detection probability peaks in the blue/green at almost 35% and is limited to a few percents in the red and near-infrared regions. When cooled down to -10°C, the 50μm diameter diode achieves a dark count rate lower than 10Hz. The afterpulsing is maintained to a low level, below 1%. The fast active quenching circuit leads to a dead time of 50ns allowing a measurement frequency of up to 20MHz. The detector, unlike legacy photon counters, does not suffer from memory effects and is not damaged by ambient light.
Programs in both the U.S. and Britain are attempting to apply staring array technology to the ship-board infrared search and track (SBIRST) problem. A prime objective is to speed processing time, the previous generation of 360 deg scanners having a refresh rate of only 0.5-1.0 Hz. Another objective is to enhance sensitivity using much longer integration times. An impediment, though, is that if all pixels of resolution angle ∅ were to be viewed simultaneously with dedicated detectors each of width w, the total net length of detector material would then have to be very large: 2πw/∅ = 1.57 m = 60" for 100 μRad resolution and 25 μm detectors. So the application of staring array technology to horizon surveillance needs some form of wide viewing technique involving a combination of asymmetric resolution, reduced resolution, split optics or LOS stepping. The present paper suggests that conventional NEI is not the preferred unit of measure for guiding design choices but that instead a form of BLIP S/N can be both simple and intuitive. This S/N unit of measure is used to compare the two main choices for how to adapt staring technology to the horizon surveillance problem.
We report here on wafer-bonded InGaAs/Si avalanche photodiodes (APDs) demonstrating very low excess noise factors that were fabricated using a high-yield, wafer-scale bonding process. The bonding interface quality was evaluated using high-resolution x-ray diffraction and dark current measurements. Measured dark currents on 20 μm diameter mesas are 25 nA and 170 nA at gains of 10 and 50, respectively. Low excess noise factors, which are predicted due to the superior noise properties of Si as a multiplication layer, were measured to be more than 3 times lower than commercial InGaAs/InP APDs at a gain of 10, and more than 9 times lower at a gain of 50. The corresponding electron/hole ionization coefficient ratio k in these devices is as low as 0.02.
Wafer-bonded avalanche photodiodes (APDs) combining InGaAs for the absorption layer and silicon for the multiplication layer have been fabricated. The reported APDs have a very low room-temperature dark current density of only 0.7 mA/cm2 at a gain of 10. The dark current level is as low as that of conventional InGaAs/InP APDs. High avalanche gains in excess of 100 are presented. The photodiode responsivity at a wavelength of 1.31 micrometers is 0.64 A/W, achieved without the use of an anti-reflection coating. The RC-limited bandwidth is 1.45 GHz and the gain-bandwidth product is 290 GHz. The excess noise factor F is much lower than that of conventional InP-based APDs, with values of 2.2 at a gain of 10 and 2.3 at a gain of 20. This corresponds to an effective ionization rate ratio keff as low as 0.02. The expected receiver sensitivity for 2.5 Gb/s operation at (lambda) = 1.31 um using our InGaAs/silicon APD is -41 dBm at an optimal gain of M = 80.
Fast-growing internet traffic volume require high data communication bandwidth over longer distances. Access network bottlenecks put pressure on short-range (SR) telecommunication systems. To effectively address these datacom and telecom market needs, low-cost, high-speed laser modules at 1310 to 1550 nm wavelengths and avalanche photodetectors are required. The great success of GaAs 850nm VCSEls for Gb/s Ethernet has motivated efforts to extend VCSEL technology to longer wavelengths in the 1310 and 1550 nm regimes. However, the technological challenges associated with materials for long wavelength VCSELs are tremendous. Even with recent advances in this area, it is believed that significant additional development is necessary before long wavelength VCSELs that meet commercial specifications will be widely available. In addition, the more stringent OC192 and OC768 specifications for single-mode fiber (SMF) datacom may require more than just a long wavelength laser diode, VCSEL or not, to address numerous cost and performance issues. We believe that photonic integrated circuits (PICs), which compactly integrate surface-emitting lasers with additional active and passive optical components with extended functionality, will provide the best solutions to today's problems. Photonic integrated circuits have been investigated for more than a decade. However, they have produced limited commercial impact to date primarily because the highly complicated fabrication processes produce significant yield and device performance issues. In this presentation, we will discuss a new technology platform of InP-based PICs compatible with surface-emitting laser technology, as well as a high data rate externally modulated laser module. Avalanche photodetectors (APDs) are the key component in the receiver to achieve high data rate over long transmission distance because of their high sensitivity and large gain- bandwidth product. We have used wafer fusion technology to achieve InGaAs/Si APDs with much greater potential than the traditional InGaAs/InP APDs. Preliminary results on their performance will be presented.
Fast-growing internet traffic volumes require high data communication bandwidth over longer distances than short wavelength (850 nm) multi-mode fiber systems can provide. Access network bottlenecks put pressure on short-range (SR) telecommunication systems. To effectively address these datacom and telecom market needs, low cost, high-speed laser modules at 1310 and 1550 nm wavelengths are required. The great success of GaAs 850 nm VCSELs for Gb/s Ethernet has motivated efforts to extend VCSEL technology to longer wavelengths in the 1310 and 1550 nm regimes. However, the technological challenges associated with available intrinsic materials for long wavelength VCSELs are tremendous. Even with recent advances in this area, it is believed that significant additional development is necessary before long wavelength VCSELs that meet commercial specifications will be widely available. In addition, the more stringent OC192 and OC768 specifications for single-mode fiber (SMF) datacom may require more than just a long wavelength laser diode, VCSEL or not, to address numerous cost and performance issues. We believe that photonic integrated circuits, which compactly integrate surface-emitting lasers with additional active and passive optical components with extended functionality, will provide the best solutions to today's problems. Photonic integrated circuits (PICs) have been investigated for more than a decade. However, they have produced limited commercial impact to date primarily because the highly complicated fabrication processes produce significant yield and device performance issues. In this presentation, we will discuss a new technology platform for fabricating InP-based photonic integrated circuits compatible with surface-emitting laser technology. Employing InP transparency at 1310 and 1550 nm wavelengths, we have created 3-D photonic integrated circuits (PICs) by utilizing light beams in both surface normal and in-plane directions within the InP-based structure. This additional beam routing flexibility allows significant size reduction and process simplification without sacrificing device performance. This innovative 3-D PIC technology platform can be easily extended to create surface-emitting lasers integrated with power monitoring detectors, micro-lenses, external modulators, amplifiers, and other passive and active components. Such added functionality can produce cost--effective solutions for the highest-end laser transmitters required for datacom and short range telecom networks, as well as fiber channels and other cost and performance sensitive applications. We present results for 1310 nm photonic IC surface-emitting laser transmitters operating at 2.5 Gbps without active thermal electric cooling.
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