We compare different designs for very high-speed (millimeter-wave) long-wavelength photodetectors, different materials for such detectors, and different ways of characterizing the speed of these devices. Experimental results are given, showing high-speed response with bandwidths beyond 50 GHz, impulse responses less than 10 ps, and detection sensitivities to 0.1 fJ in packaged devices. Discussed is the inherent bandwidth-efficiency limit in conventional p-i-n detectors, which is then compared to theoretical and experimental results for waveguide-geometry detectors.

Ultrawide-band long-wavelength p-i-n photodetectors

Optical, crystallographic, and transport properties of nominally undoped n‐type and Zn doped p‐type Gax In1−xAs /InP (0.44<x<0.49) grown by liquid phase epitaxy (LPE), vapor phase epitaxy (VPE), and metal organic chemical vapor deposition (MOCVD) have been studied and related to the different growth methods. Samples grown by LPE show in general much larger luminescence intensities than the VPE samples with similar impurity concentration and less structural and compositional inhomogeneities. Peaks related to free and bound excitons and to different impurities are found in the photoluminescence and absorption spectra of the undoped samples. The binding energy of the exciton is determined to be 2.1±0.1 meV, in agreement with hydrogenic theory. A longitudinal optical (LO) phonon energy of 32±0.5 meV is derived from LO‐phonon replica of the exciton line. The dependence of the energy gap at T=2 K from the solid solution composition in the range xGa =45%–49% is determined yielding a bowing parameter of C=0.475 a...

Optical and crystallographic properties and impurity incorporation of GaxIn1−xAs (0.44<x<0.49) grown by liquid phase epitaxy, vapor phase epitaxy, and metal organic chemical vapor deposition

This paper describes the applicability of subcarrier multiplexing to lightwave multiple-access networks. It is shown how currently available microwave and lightwave components can be used, by using subcarrier multiplexing, to provide high-capacity networks. For example, the proposed multiple-access network can support 1024 users at a continuous bit rate of 1.5 Mbit/s, per user.

Subcarrier multiplexing for multiple-access lightwave networks

Two synchronous multiple access schemes, TDMA and CDMA, are proposed for fiber optic networks using optical signal processing. Network synchronization is achieved by using a central modelocked laser which also serves as the source for each station. The data are converted into a high-bandwidth optical signal using electrooptic modulators. The accessing schemes use optical fiber delay lines. The feasibility of these schemes is discussed.

Ultrafast All-Optical Synchronous Multiple Access Fiber Networks

Receiver design for high-speed ptical-fiber systems

At the wavelength of 1.3 μm, fiber loss and dispersion are sufficiently small that many lightwave communications applications can use simple and reliable LED transmitters and PIN photodiode receivers without avalanche gain. Bit rates can be as high as several hundred Mb/s. With new high-speed devices based on III–V semiconductors and microwave silicon IC technology, we have designed two fully retimed optical regenerators that operate at 1.3 μm and at bit rates of 44.7 and 274 Mb/s to study the potential of the LED-pin approach. A detailed analysis of the baseband characteristics of the LED, the fiber, and the receiver leads to an overall equalization approach that minimizes receiver noise. The success of this performance optimization is corroborated by bit-error measurements under simulated system conditions. The results suggest repeaterless operation over distances up to 24 km at 44.7 Mb/s and 8 km at 274 Mb/s for a cable loss of 1 dB/km and a bandwidth of 1000 MHz·km. The use of lasers in such multimode fiber sytems would permit larger margin allocations and penalties than those chosen for LED systems, but would not lead to substantially longer repeater spacings.

High-speed digital lightwave communication using LEDs and PIN photodiodes at 1.3 μm

Long-wavelength back-illuminated PIN photodiodes capable of detecting optical signals at multigigabit modulation rates have been fabricated and tested in a stripline circuit. A transit-time-limited response time of about 30 ps has been realised in a 25 μm-diameter diode.

Very-high-speed back-illuminated InGaAs/InP PIN punch-through photodiodes

Small-area Zn-diffused homojunction InGaAs/InP p-i-n photodetectors for wavelengths up to 1.65 μm have been fabricated in a back-illuminated configuration. The dark current is 5 nA and the capacitance is 0.3 pF at -10 V bias; the quantum efficiency is 65% without a.r. coatings. As 1.31 μm detectors in a p-i-n/f.e.t. receiver preamplifier, the diodes have provided a receiver sensitivity of -46.7 dBm at 45 Mb/s and -36 dBm at 274 Mb/s for 10-9 error rate.

Small area ingaas/inp p-i-n photodiodes: fabrication, characteristics and performance of devices in 274 mb/s and 45 mb/s lightwave receivers at 1.31 μm wavelength

We describe the fabrication and characteristics of a small‐area (diameter ≃20 μm) InP/InGaAs heterojunction phototransistor, a promising photodetector/preamplifier for long‐wavelength optical receivers. The high sensitivity (hfe ≃100 at 20‐nW incident power) and small junction capacitance (≲0.2 pF) of the device combine to produce a gain‐bandwidth product in excess of 1.7 GHz.

Small-area high-speed InP/InGaAs phototransistor

A GaAs f.e.t. transimpedance front-end amplifier was built and operated as part of a regenerator at 274 Mb/s. The noise characteristics were optimised for operation with a Ge photodiode at 1.32 μm, but were measured at 0.82 μm to compare Si and Ge photodiodes. The amplifier input capacitance was 3.2 pF with the Si p-i-n diode and 4.6 pF with the Ge diode. At 0.82 μm, we measured a sensitivity for 10−9 error rate of about −35 dBm with the Si diode and −32 dBm with the Ge diode. We predict a sensitivity of −34 dBm at 1.32 μm.

K. Ogawa

Papers

High-speed digital lightwave communication using LEDs and PIN photodiodes at 1.3 μm

Very-high-speed back-illuminated InGaAs/InP PIN punch-through photodiodes

Small area ingaas/inp p-i-n photodiodes: fabrication, characteristics and performance of devices in 274 mb/s and 45 mb/s lightwave receivers at 1.31 μm wavelength

Small-area high-speed InP/InGaAs phototransistor

GaAs f.e.t. transimpedance front-end design for a wideband optical receiver