Er/sup 3+/ glass waveguide amplifier at 1.5 mu m on silicon

Highly Er/sup 3+/-doped sodium calcium silicate glass waveguide was fabricated on oxidised silicon wafers. An Er/sup 3+/ absorption of 8.5 dB/cm was measured at 1.53 mu m, whereas transmission loss outside the Er/sup 3+/ absorption band was estimated to be approximately 1 dB/cm. By pumping the waveguide with 120 mW of power at 975 nm the 1.53 mu m signal intensity was enhanced by 21 dB.<>     

Pixelless imaging device using optical up-converter

A pixelless imaging device based on optical wavelength conversion was designed and fabricated. The up-converter consisted of an integrated InGaAs/InP PIN photodetector and an InGaAsP/InP light-emitting diode (LED) epitaxially grown on a single InP substrate. Incoming 1.5 /spl mu/m optical radiation was absorbed by the p-i-n detector and generated a photocurrent. The resultant photocurrent was used to bias the LED that emitted at 1 /spl mu/m, which could be detected by conventional silicon charge coupled device. Pixelless imaging by the device has been demonstrated at room temperature.     

A dependency of quantum efficiency of silicon CMOS n/sup +/pp/sup +/ LEDs on current density

A dependency of quantum efficiency of nn/sup +/pp/sup +/ silicon complementary metal-oxide-semiconductor integrated light-emitting devices on the current density through the active device areas is demonstrated. It was observed that an increase in current density from 1.6/spl times/10/sup +2/ to 2.2/spl times/10/sup +4/ A/spl middot/cm/sup -2/ through the active regions of silicon n/sup +/pp/sup +/ light-emitting diodes results in an increase in the external quantum efficiency from 1.6/spl times/10/sup -7/ to 5.8/spl times/10/sup -6/ (approximately two orders of magnitude). The light intensity correspondingly increase from 10/sup -6/ to 10/sup -1/ W/spl middot/cm/sup -2//spl middot/mA (approximately five orders of magnitude). In our study, the highest efficiency device operate in the p-n junction reverse bias avalanche mode and utilize current density increase by means of vertical and lateral electrical field confinement at a wedge-shaped n/sup +/ tip placed in a region of lower doping density and opposite highly conductive p/sup +/ regions.     

1.58-/spl mu/m broad-band erbium-doped tellurite fiber amplifier

This paper describes the development of a 1.58-/spl mu/m broad-band and gain-flattened erbium-doped tellurite fiber amplifier (EDTFA). First, we compare the spectroscopic properties of various glasses including the stimulated emission cross sections of the Er/sup 3+4/ I/sub 13/2/ /sup 4/I/sub 15/2/ transition and the signal excited-state absorption (ESA) cross sections of the Er/sup 3+4/ I/sub 13/2/ - /sup 4/I/sub 9/2/ transition. We detail the amplification characteristics of a 1.58-/spl mu/m-band EDTFA designed for wavelength-division-multiplexing applications by comparing it with a 1.58-/spl mu/m-band erbium-doped silica fiber amplifier. Furthermore, we describe the 1.58-/spl mu/m-band gain-flattened EDTFA we developed using a fiber-Bragg-grating-type gain equalizer. We achieved a gain of 25.3 dB and a noise figure of less than 6 dB with a slight gain excursion of 0.6 dB over a wide wavelength range of 1561-1611 nm. The total output power of the EDTFA module was 20.4 dBm and its power conversion efficiency reached 32.8%.     

High detectivity InGaN-GaN multiquantum well p-n junction photodiodes

InGaN-GaN multiquantum well (MQW) p-n junction photodiodes with semi-transparent Ni-Au electrodes were fabricated and characterized. It was found that the fabricated InGaN-GaN p-n junction photodiodes exhibit a 20-V breakdown voltage and a photocurrent to dark current contrast ratio of /spl sim/10/sup 5/ when a 0.4-V reverse bias was applied. The peak responsivity at 380 nm was 1.28 and 1.76 A/W with a 0.1- and 3-V applied reverse bias, respectively. Furthermore, an internal gain was found from our InGaN-GaN MQW p-n junction photodiodes possibly due to the long-lifetime of GaN based materials. Also, it was found that the low frequency noise of our photodiodes was dominated by the 1/f type noise. For a given bandwidth of 500 Hz, the corresponding noise equivalent power and normalized detectivity D/sup */ were found to be 6.34/spl times/10/sup -13/ W and 4.45/spl times/10/sup 11/ cm/spl middot/Hz/sup 0.5/ W/sup -1/, respectively.     

Continuous-wave operation of GaInAsSb-GaSb type-II ridge waveguide lasers emitting at 2.8 /spl mu/m

We have realized compressively strained GaInAsSb-GaSb type-II double quantum-well lasers with an emission wavelength of 2.8 /spl mu/m. Using broad area devices, an internal absorption of 9.8 cm/sup -1/ and an internal quantum efficiency of 0.57 is determined. For the increase of the threshold current with temperature, a T/sub 0/ of 44 K is obtained. Narrow ridge waveguide lasers show continuous-wave laser operation at temperatures up to 45 /spl deg/C, with room-temperature (RT) threshold current of 37 mA. At RT, the maximum optical output power per facet of an uncoated 800/spl times/7 /spl mu/m/sup 2/ ridge waveguide laser exceeds 8 mW.     

High-efficiency 1.3 /spl mu/m InAsP-GaInP MQW electroabsorption waveguide modulators for microwave fiber-optic links

High-efficiency electroabsorption waveguide modulators have been designed and fabricated using strain-compensated InAsP-GaInP multiple quantum wells at 1.32-/spl mu/m wavelength. A typical 200-/spl mu/m-long modulator exhibits a fiber-to-fiber optical insertion loss of 9 dB and an optical saturation intensity larger than 10 mW. The 3-dB electrical bandwidth is in excess of 20 GHz with a 50-/spl Omega/ load termination. When used in an analog microwave fiber-optic link without amplification, a RF link efficiency as high as -38 dB is achieved at 10 mW input optical carrier power. These analog link characteristics are the first reported using MQW electroabsorption waveguide modulators at 1.32 /spl mu/m.     

Design and fabrication of zinc oxide thin-film ridge waveguides on silicon substrate with ultraviolet amplified spontaneous emission

Zinc oxide (ZnO) thin-film ridge waveguides have been designed and fabricated on n-type (100) silicon substrate. A filtered cathodic vacuum arc technique is used to deposit high-crystal-quality ZnO thin films on lattice-mismatched silicon substrates at 230/spl deg/C. A ridge waveguide of width /spl sim/2 /spl mu/m and height /spl sim/0.1 /spl mu/m is defined on the ZnO thin film by plasma etching. Room-temperature amplified spontaneous emission is observed with peak wavelength at /spl sim/385 nm under 355-nm optical excitation. It is found that the net optical gain of the ZnO thin-film ridge waveguides can be as large as 120 cm/sup -1/ at a pump intensity of /spl sim/1.9 MW/cm/sup 2/.     

Thermo-optical modulation at /spl lambda/=1.5 /spl mu/m in an /spl alpha/-SiC-/spl alpha/-Si-/spl alpha/-SiC planar guided-wave structure

A planar waveguide based on an amorphous silicon-amorphous silicon carbide heterostructure is proposed for the realization of passive and active optical components at the wavelengths /spl lambda/=1.3-1.5 /spl mu/m. The waveguide has been realized by low temperature plasma enhanced chemical vapor deposition and is compatible with the standard microelectronic technologies. Thermo-optical induced modulation at /spl lambda/=1.5 /spl mu/m is demonstrated in this waveguide. Numerical simulations predict that operation frequencies of about 3 MHz are possible. The measurements have also allowed the determination of the previously unknown thermo-optical coefficient of undoped amorphous silicon at this wavelength.     

Er-doped glass ridge-waveguide amplifiers fabricated with a collimated sputter deposition technique

We report a new fabrication process for Er-doped glass ridge waveguides. The process does not require etching of an Er-doped film in defining the lateral dimension of a waveguide, but involves a liftoff process using polyimide as a sacrificial layer. An Er-doped soda-lime silicate glass film (1.5 /spl mu/m thick) was deposited at 350/spl deg/C using a collimated sputtering technique. Conventional sputtering techniques have been known to be incompatible with a liftoff process. The collimated sputtering, however, allowed us easy liftoff of Er-doped films, and produced well-defined ridges with smooth surface profiles. A 1.7-cm-long waveguide thus fabricated shows a 1.55-/spl mu/m signal enhancement of 15.4 dB with a 980-nm pump power of 40 mW. This enhancement fully compensates for both Er absorption and waveguide losses, and results in a gain of 7.2 dB.     

16 W continuous-wave output power from 100 /spl mu/m-aperture laser with quantum well asymmetric heterostructure

16 W continuous-wave room temperature front facet output optical power and 74% wallplug efficiency were attained in 100 /spl mu/m-aperture 1.06 /spl mu/m-emitting laser diodes with 2-3 mm cavity length. The lasers are based on AlGaAs/GaAs/InGaAs quantum well asymmetric heterostructures with 1.7 /spl mu/m-thick waveguide having 0.34 cm/sup -1/ internal optical loss.     

InGaAs-InP mesa DHBTs with simultaneously high f/sub /spl tau// and f/sub max/ and low C/sub cb//I/sub c/ ratio

We report an InP-InGaAs-InP double heterojunction bipolar transistor (DHBT), fabricated using a conventional triple mesa structure, exhibiting a 370-GHz f/sub /spl tau// and 459-GHz f/sub max/, which is to our knowledge the highest f/sub /spl tau// reported for a mesa InP DHBT-as well as the highest simultaneous f/sub /spl tau// and f/sub max/ for any mesa HBT. The collector semiconductor was undercut to reduce the base-collector capacitance, producing a C/sub cb//I/sub c/ ratio of 0.28 ps/V at V/sub cb/=0.5 V. The V/sub BR,CEO/ is 5.6 V and the devices fail thermally only at >18 mW//spl mu/m/sup 2/, allowing dc bias from J/sub e/=4.8 mA//spl mu/m/sup 2/ at V/sub ce/=3.9 V to J/sub e/=12.5 mA//spl mu/m/sup 2/ at V/sub ce/=1.5 V. The device employs a 30 nm carbon-doped InGaAs base with graded base doping, and an InGaAs-InAlAs superlattice grade in the base-collector junction that contributes to a total depleted collector thickness of 150 nm.     

Erbium spectroscopy and 1.5-/spl mu/m emission in KGd(WO/sub 4/)/sub 2/: Er,Yb single crystals

We grew good-optical-quality KGd(WO/sub 4/)/sub 2/ single crystals doped with erbium and ytterbium ions at several concentrations of dopants using the top-seeded-solution growth slow-cooling method (TSSG). We performed the spectroscopic characterization of this material related to the 1.5-mm infrared emission of erbium which is interesting for laser applications. To do this, we carried out polarized optical absorption at room temperature (RT) and at low temperature (6 K) and performed luminescence studies of the emission and lifetime. We obtained the 1.5-mm emission of erbium after selective laser pump excitation of the ytterbium ion and energy transfer between the two ions. The maximum emission cross section for 1.5 mm was about 2.56/spl times/10/sup -20/ cm/sup 2/ for the polarization of light with the electric field parallel to the N/sub m/ principal optical direction. This value was higher than for other erbium-doped materials with application in solid-state lasers such as LiYF/sub 4/:Er(YLF:Er), Y/sub 3/Al/sub 5/O/sub 12/:Er(YAG:Er), YAlO/sub 3/:Er, and Al/sub 2/O/sub 3/:Er.     

InGaAs-AlAs-AlAsSb coupled quantum well intersubband transition all-optical switch with low switching energy for OTDM systems

We report a novel intersubband transition all-optical switch with low switching energy using InGaAs-AlAs-AlAsSb coupled double quantum wells (C-DQWs) with AlAs spacer layers. Very low saturation energy density of 34 fJ//spl mu/m/sup 2/ was observed for bulk transmittance with wavelength of 1.62 /spl mu/m. Using a waveguide, whose core is 93 periods of the C-DQWs, an all optical switch with a low switching energy of 10 pJ for 10-dB extinction ratio was realized.     

Optical and electrical properties of nanostructured metal-silicon-metal photodetectors

We report an experimental evaluation of the performance of silicon (Si) photodetectors incorporating one-dimensional (1-D) arrays of rectangular and triangular-shaped nanoscale structures within their active regions. A significant (/spl sim/2/spl times/) enhancement in photoresponse is achieved in these devices across the 400- to 900-nm spectral region due to the modification of optical absorption properties that results from structuring the Si surface on physical optics scales smaller than the wavelength, which both reduces the reflectivity and concentrates the optical field closer to the surface. Both patterned (triangular and rectangular lineshape) and planar Ni-Si back-to-back Schottky barrier metal-semiconductor-metal photodetectors on n-type (/spl sim/5/spl times/10/sup 14/ cm/sup -3/) bulk Si were studied. 1-D /spl sim/50-250-nm linewidth, /spl sim/1000-nm depth, grating structures were fabricated by a combination of interferometric lithography and dry etching. The nanoscale grating structures significantly modify the absorption, reflectance, and transmission characteristics of the semiconductor: air interface. These changes result in improved electrical response leading to increased external quantum efficiency (from /spl sim/44% for planar to /spl sim/81% for structured devices at /spl lambda/=700 nm). In addition, a faster time constant (/spl sim/1700 ps for planar to /spl sim/600 ps for structured at /spl lambda/=900 nm) is achieved by increasing the absorption near the surface where the carriers can be rapidly collected. Experimental quantum efficiency and photocurrents results are compared with a theoretical photocurrent model based on rigorous coupled-wave analysis of nanostructured gratings.     

1.5-/spl mu/m InGaAsP-InP slab-coupled optical waveguide lasers

We report the demonstration of high-power semiconductor slab-coupled optical waveguide lasers (SCOWLs) operating at a wavelength of 1.5 /spl mu/m. The lasers operate with large (4/spl times/8 /spl mu/m diameter) fundamental mode and produce output power in excess of 800 mW. These structures have very low loss (/spl sim/0.5 cm/sup -1/) enabling centimeter-long devices for efficient heat removal. The large fundamental mode allows 55% butt-coupling efficiency to standard optical fiber (SMF-28). Comparisons are made between SCOWL structures having nominal 4- and 5-/spl mu/m-thick waveguides.     

Propagation-mode-controlled fabrication of self-written waveguide in photosensitive polyimide for single-mode operation

We have developed a new fabrication method of single-mode self-written waveguide by controlling the propagation mode in an optical fiber. This method is very appropriate for repeatable fabrication of the single-mode self-written waveguide. Since a Gaussian-like near-field pattern is required for the fabrication of a tiny and uniform waveguide core, the propagation mode in a conventional optical communication fiber was controlled by coupling with an optical fiber having 3-/spl mu/m core, which shows a single-mode operation at visible wavelength region. Single-mode propagation at optical communication wavelength was confirmed for the fabricated self-written waveguide. The evaluated core diameter of the self-written waveguide was /spl sim/9.5 /spl mu/m.     

1.65 /spl mu/m-band optical amplification with Er/sup 3+/-doped fluorozirconate fibre using 0.8 /spl mu/m upconversion pumping

In order to expand the available bandwidth for wavelength division multiplexing transmission systems, a 1.65 /spl mu/m-band optical fibre amplifier with Er/sup 3+/-doped fluorozirconate fibre using 0.8 /spl mu/m upconversion pumping has been demonstrated. The positive gain, 3.8 dB, is the first ever achieved by means of (/sup 2/H/sub 11/2/, /sup 4/S/sub 3/2/) /spl rarr/ /sup 4/I/sub 9/2/ stimulated emission transition.     

Effect of the doping level of a p-cladding layer on the performance of GaAs-AlGaAs multiquantum-well lasers

CW performance of multiquantum-well (MQW) GaAs-AlGaAs lasers operating near 850 nm at 300 K is investigated as a function of the doping level in the p-cladding layer. Laser structures have been grown by metal-organic chemical vapor deposition using Zn diethyl as a carrier for acceptor dopant. An undoped sublayer (setback) has been introduced to separate the heavily doped part of the cladding from the mode volume. The doping level of zinc ranges from 4/spl times/10/sup 17/ to 6.5/spl times/10/sup 18/cm/sup -3/. Along with this increase of the doping level, the threshold current density increases from 370 to 612 A/cm/sup 2/ whereas the slope efficiency of the laser increases from 0.71 to 1.33 W/A with an improvement of the characteristic temperature constant T/sub 0/ from 150 to 250 K. At the highest level of doping, the internal quantum yield is found to be close to unity and optical losses are as low as 1.36 cm/sup -1/. An increase of the stable single-mode output is also obtained in 3-/spl mu/m-wide ridge-waveguide diodes up to /spl sim/180 mW.     

1.5 /spl mu/m GaInNAs semiconductor saturable absorber for passively modelocked solid-state lasers

Fully self-starting and passively modelocking of a 1.5 /spl mu/m solid-state laser with a GaInNAs semiconductor saturable absorber mirror (SESAM) has been demonstrated for the first time. A saturation fluence of 20 /spl mu/J/cm/sup 2/, a modulation depth of 0.39% and a fast temporal decay of 18 ps were measured. These well-suited nonlinear optical SESAM parameters allowed for self-starting and passive modelocking of a diode-pumped Er:Yb:glass laser at 1.534 /spl mu/m with a pulse duration of 5 ps at 61 MHz.