A.G. Dentai

Nd:YAG single‐crystal fiber laser: Room‐temperature cw operation using a single LED as an end pump

cw laser action has been obtained using as‐grown single‐crystal Nd:YAG fibers end‐pumped by a single high‐radiance LED. The fibers were 0.5 cm long and 80 μm in diameter, and the diameter of the LED luminous area was 85 μm. The lowest cw laser threshold was observed at a diode drive current of 45 mA.

Low-threshold InGaAsP ridge waveguide lasers at 1.3 µm

The ridge waveguide configuration is shown to provide reliable low-threshold fundamental-transverse-mode lasers that are readily fabricated. Two variants are described: in the simple ridge laser, the 1.3 μm bandgap active layer is sandwiched between InP layers and in the cladded ridge, the active layer is surrounded by 1.1 μm bandgap InGa AsP. Thresholds as low as 34 mA and efficiencies as high as 66 percent are observed. Output power is linear to more than 12 mW. Several lasers have been operated at 30°C for over 1500 h without measurable degradation. Selected lasers exhibit stabilized longitudinal mode behavior over extended temperature and current ranges. The potential manufacturability of this device is its most attractive feature.

Small‐area high‐speed InP/InGaAs phototransistor

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.

Optically induced catastrophic degradation in InGaAsP/InP layers

Laser‐induced catastrophic degradation in InGaAsP layers has been investigated. Catastrophic dark line (CDL) defects are generated at the spontaneous radiation flux in excess of 100 MW/cm2, significantly higher than in similar GaAlAs structures. In contrast to CDL’s in GaAlAs these dark lines are shown to be due to localized melting at material defects and not at cleaved mirror facets. In view of the very high power threshold this type of catastrophic degradation should be of limited importance for the InGaAsP lasers.

Dual‐wavelength demultiplexing InGaAsP photodiode

We report the successful operation of a new photodiode structure capable of detecting and demultiplexing two wavelength bands simultaneously. Wavelength discrimination is achieved with a multilayer structure that incorporates p‐n junctions in two InxGa1−xAsyP1−y layers having different band gaps. In initial devices ’’crosstalk’’ between the photoresponses is less than −10 dB at each response peak.

InP/InGaAs heterojunction phototransistor with integrated light emitting diode

We describe a novel heterojunction phototransistor structure which incorporates an integrated light emitting diode (LED) to provide an optically coupled dc bias current. A drive current of 6 mA through the LED results in a threefold decrease in the rise time (from 210 to 70 ns) and a twofold increase in the gain (from 30 to 60). The optically coupled dc bias can be adjusted to optimize the bandwidth and signal to noise ratio for particular applications.

High avalanche gain in small‐area InP photodiodes

Extremely high avalanche gains, up to 2×104, accompanied by low leakage current and moderate excess avalanche noise, have been observed in small areas of diffused p‐n junctions in undoped n‐type InP. The results imply that dislocation densities much less than 104 cm−2 probably will be a prerequisite for practical long‐wavelength avalanche photodiodes in the InGaAsP/InP system.

Large-area back-illuminated InGaAs/InP photodiodes for use at 1 to 1.6 μm wavelength

Abstract Back-illuminated PIN photodiodes with active areas 1 mm in diameter have been made from LPE-grown InGaAs/InP. The diodes have photoresponse, leakage and stability properties which suggest that they may be superior to germanium photodiodes for many general-purpose long-wavelength applications.

A comparison of ’’normal’’ lasers and lasers exhibiting light jumps

We have done a comparative examination of two sets of lasers, one set exhibiting a light jump and unusually low pulsation frequencies and another set of ’’normal’’ lasers which do not show these phenomena. Our characterization involved measurements of the near field and far field, the emission spectrum versus current, and the pulsation frequency versus current. These measurements did not reveal any major differences between the two types of lasers except that the pulsation frequencies tend to be lower when light jumps are present. In addition, the laser facets were stained with a dilute A/B etch and inspected with a scanning electron microscope. This showed that the distinction between the two types of lasers may be the position of the tail of the proton bombardment with respect to the active layer.

High‐speed junction‐depleted Ga0.47In0.53As photoconductive detectors

A high‐speed junction‐depleted Ga0.47In0.53As photoconductive detector without making use of radiation damage to the sample is reported. The detector has a light absorbing region in the n−layer of an unbiased p‐n junction. As a result of the built‐in field associated with the p‐n junction, the carriers generated far from the surface were removed, leading to a picosecond response time. When tested by 100‐ps, 1.55‐μm light pulses, the detector showed a fall time of 90 ps with an external gain >1.3 (no antireflection coating). Receiver sensitivity at 1 Gb/s was −25.3 dBm at 1.55 μm and an error rate of 10−9.