Second-order nonlinearity of a disazo dye attached polymer

Second-order optical nonlinearity of a disazo dye attached polymer was investigated. The optical loss of the film is 1.5 dB/cm at 633 nm. The second-order nonlinear coefficient chi /sup (2)/ of the poled film is comparable to that of lithium niobate at 1.55 mu m. The chi /sup (2)/ is greater than that of a monoazo dye attached polymer throughout the fundamental wavelength of 1.06-1.70 mu m.<>     

Large nonlinear optical effect in an InGaAs/InAlAs multiquantum well waveguide

All-optical refractive nonlinearity in a passive InGaAs/InAlAs multiquantum well waveguide is evaluated for TE and TM modes at 1.55 mu m wavelength and room temperature. A quarter wavelength change in the optical path length is observed at an input pump light power of 6.5 mW for 1.47 mu m wavelength in a 960 mu m long device. Nonlinear refractive index n/sub 2/ is evaluated to be -1.2*10/sup 6/ and -0.5*10-6cm/sup 2//W for the TE and the TM modes, respectively.<>     

A high-speed ITO-InAlAs-InGaAs Schottky-barrier photodetector

A high-speed and high-sensitivity vertical indium-tin-oxide-InAlAs-InGaAs Schottky barrier photodetector has been designed, fabricated, and characterized. The devices had dark current densities as low as 8.87/spl times/10/sup -5/ A/cm/sup -2/ at an applied bias of 5 V. The responsivity for all the devices tested ranged from 0.55-0.60 A/W at a wavelength of 1.31 /spl mu/m, and 0.563-0.583 A/W at 1.55 /spl mu/m. The 15-/spl mu/m diameter devices exhibited a -3 dB bandwidth of 19 and 25 GHz at a wavelength of 1.55 /spl mu/m and an applied bias of 5 and 10 V, respectively. These are the best values of responsivity and bandwidth for a vertical InGaAs-based Schottky-barrier photodetector reported to date.     

Optical parametric generation covering the sodium D/sub 1/, D/sub 2/ lines from a 532-nm pumped periodically poled lithium niobate (PPLN) crystal with ionic-nonlinearity enhanced parametric gain

We report optical parametric generation from a 532-nm-pumped periodically poled lithium niobate with a wavelength spectrum covering the sodium D/sub 1/, D/sub 2/ wavelengths 589.6 and 589.0 nm. Despite the 8 cm/sup -1/ attenuation at the 5.45 /spl mu/m idler wavelength, the PPLN generates a 9 /spl mu/J/pulse energy near the 589-nm sodium wavelength when pumped by a 130 /spl mu/J/pulse frequency-doubled Nd:YAG Q-switched laser. The observed effective nonlinear coefficient is about 40% higher than its value at the visible and near infrared wavelengths. We believe that this is the first observation of ionic susceptibility enhanced parametric gain in the mid-infrared absorption region of lithium niobate.     

Observation of self-lensing in a 4BCMU-polydiacetylene, thin-film waveguide

Strong self-lensing effects have been observed when propagating 35 ps duration, 1.06 mu m wavelength pulses over 5-10 mm distance through thin-film slab waveguides formed from 4BCMU-polydiacetylene. The results are consistent with a negative nonlinear refractive index coefficient (n/sub 2/) of magnitude 1-2*10/sup -13/ cm/sup 2/ W/sup -1/.<>     

InAs-InAlGaAs quantum dot DFB lasers based on InP [001]

The InAs-InAlGaAs quantum dot (QD) lasers with the InAlGaAs-InAlAs material system were fabricated on distributed feedback (DFB) grating structures on InP [001]. The single-mode operation of InAs-InAlGaAs QD DFB lasers in continuous-wave mode was successfully achieved at the emission wavelength of 1.564 /spl mu/m at room temperature. This is the first observation on the InP-based QD lasers operating around the emission wavelength window of 1.55 /spl mu/m. The threshold current density of the InAs-InAlGaAs QD DFB laser with a cavity length of 1 mm and a ridge width of 3 /spl mu/m, in which one of the cleaved facets was coated with 95% high-reflection, was 1.23 kA/cm/sup 2/ (176 A/cm/sup 2/ for single QD layer). The sidemode suppression ratio value of the QD DFB laser was as high as 42 dB at the driving current of 100 mA.     

Room-temperature continuous-wave 1.55 /spl mu/m GaInNAsSb laser on GaAs

The first low-threshold 1.55 /spl mu/m lasers grown on GaAs are reported. Lasing at 1.55 /spl mu/m was observed from a 20/spl times/2400 /spl mu/m as-cleaved device with a room-temperature continuous-wave threshold current density of 579 A/cm/sup 2/, external efficiency of 41%, and 130 mW peak output power. The pulsed threshold current density was 550 A/cm/sup 2/ with >600 mW peak output power.     

Minimal group refractive index dispersion and gain evolution in ultra-broad-band quantum cascade lasers

The group refractive index dispersion in ultra-broad-band quantum cascade (QC) lasers has been determined using Fabry-Perot spectra obtained by operating the lasers in continuous wave mode below threshold. In the wavelength range of 5-8 /spl mu/m, the global change of the group refractive index is as small as +8.2 /spl times/ 10/sup -3/ /spl mu/m/sup -1/. Using the method of Hakki and Paoli (1975), the subthreshold gain of the lasers has furthermore been measured as a function of wavelength and current. At the wavelength of best performance, 7.4 /spl mu/m, a modal gain coefficient of 16 cm/spl middot/kA/sup -1/ at threshold and a waveguide loss of 18 cm/sup -1/ have been estimated. The gain evolution confirms an earlier assumption that cross-absorption restricted laser action to above 6 /spl mu/m wavelength.     

Influence of scattering and two-photon absorption on the optical loss in GaAs-Al/sub 2/O/sub 3/ nonlinear waveguides measured using femtosecond pulses

The influence of scattering and two-photon absorption on the optical loss in GaAs-Al/sub 2/O/sub 3/ semiconductor nonlinear waveguides has been studied using femtosecond pulses. By deploying a scattering technique, loss coefficients were evaluated over an extended wavelength range of 1.3-2.1 /spl mu/m in the near-infrared. A systematic study involving intensity and wavelength dependence of the loss revealed the presence of two-photon absorption for wavelengths below 1.6 /spl mu/m. A simple nonlinear transmission study enabled the separation of the two-photon absorption coefficient from scattering and linear absorption. The calculated two-photon absorption coefficients were /spl sim/9-20 cm/GW.     

GaInAsSb/GaSb pn photodiodes for detection to 2.4 mu m

Ga/sub 0.77/In/sub 0.23/As/sub 0.20/Sb/sub 0.80//GaSb pn heterojunction photodiodes have been prepared by liquid phase epitaxy. They exhibit a long-wavelength threshold of 2.4 mu m. The room-temperature dark current at V=-0.5 V is 3 mu A (10 mA/cm/sup 2/) and the external quantum efficiency is around 40% in the wavelength range 1.75-2.25 mu m. The estimated detectivity D* at 2.2 mu m is 8.8*10/sup 9/ cm Hz/sup 1/2/ W/sup -1/.<>     

Confinement loss and nonlinearity analysis of air-guiding modified honeycomb photonic bandgap fibers

Air-guiding photonic bandgap fibers based on a modified honeycomb lattice have been numerically investigated through the finite element method. Results confirm that an extra hole in the unit cell of a honeycomb lattice can be exploited to enlarge the photonic bandgap, allowing air-guiding with confinement losses lower than 0.1 dB/km and nonlinear coefficient lower than 3.5/spl middot/10/sup -3/(W/spl middot/km)/sup -1/ at 1.55 /spl mu/m.     

Simple measurement of carrier induced refractive-index change in InGaAsP PIN ridge waveguide structures

The carrier induced refractive-index change Delta n in integrated InGaAsP 1.30 mu m interferometer structures is evaluated by 1.55 mu m transmission measurements. At carrier concentrations N from 8*10/sup 16//cm/sup 3/ to 3*10/sup 18//cm/sup 3/ a value of Delta n/N=-1*10/sup -20/ cm/sup 3/ is obtained. A good agreement of the experimental results with theoretical predictions on bandfilling, plasma effect and bandgap shrinkage is demonstrated.<>     

A resonant tunneling quantum-dot infrared photodetector

A novel device-resonant tunneling quantum-dot infrared photodetector-has been investigated theoretically and experimentally. In this device, the transport of dark current and photocurrent are separated by the incorporation of a double barrier resonant tunnel heterostructure with each quantum-dot layer of the device. The devices with In/sub 0.4/Ga/sub 0.6/As-GaAs quantum dots are grown by molecular beam epitaxy. We have characterized devices designed for /spl sim/6 /spl mu/m response, and the devices also exhibit a strong photoresponse peak at /spl sim/17 /spl mu/m at 300 K due to transitions from the dot excited states. The dark currents in the tunnel devices are almost two orders of magnitude smaller than those in conventional devices. Measured values of J/sub dark/ are 1.6/spl times/10/sup -8/ A/cm/sup 2/ at 80 K and 1.55 A/cm/sup 2/ at 300 K for 1-V applied bias. Measured values of peak responsivity and specific detectivity D/sup */ are 0.063 A/W and 2.4/spl times/10/sup 10/ cm/spl middot/Hz/sup 1/2//W, respectively, under a bias of 2 V, at 80 K for the 6-/spl mu/m response. For the 17-/spl mu/m response, the measured values of peak responsivity and detectivity at 300 K are 0.032 A/W and 8.6/spl times/10/sup 6/ cm/spl middot/Hz/sup 1/2//W under 1 V bias.     

Optimized second-harmonic generation in quantum cascade lasers

Optimized second-harmonic generation (SHG) in quantum cascade (QC) lasers with specially designed active regions is reported. Nonlinear optical cascades of resonantly coupled intersubband transitions with giant second-order nonlinearities were integrated with each QC-laser active region. QC lasers with three-coupled quantum-well (QW) active regions showed up to 2 /spl mu/W of SHG light at 3.75 /spl mu/m wavelength at a fundamental peak power and wavelength of 1 W and 7.5 /spl mu/m, respectively. These lasers resulted in an external linear-to-nonlinear conversion efficiency of up to 1 /spl mu/W/W/sup 2/. An improved 2-QW active region design at fundamental and SHG wavelengths of 9.1 and 4.55 /spl mu/m, respectively, resulted in a 100-fold improved external linear-to-nonlinear power conversion efficiency, i.e. up to 100 /spl mu/W/W/sup 2/. Full theoretical treatment of nonlinear light generation in QC lasers is given, and excellent agreement with the experimental results is obtained. For the best structure, a second-order nonlinear susceptibility of 4.7/spl times/10/sup -5/ esu (2/spl times/10/sup 4/pm/V) is calculated, about two orders of magnitude above conventional nonlinear optical materials and bulk III-V semiconductors.     

Waveguided electro-optical intensity modulation in a Si/Ge/sub x/Si/sub 1-x//Si heterojunction bipolar transistor

Optical phase-and-amplitude modulation at 1.55 mu m in an electro-optic guided-wave Si/Ge/sub 0.2/Si/sub 0.8//Si HBT is investigated using computer-aided modelling and simulation. At an injection of 10/sup 19/ electrons per cm/sup 3/, an intensity modulation of 10 dB is predicted for an active length of 390 mu m.<>     

Low-temperature MBE-grown In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As/InP optical waveguides

The MBE growth of In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As ( lambda /sub g/=1.06 mu m) layers in the temperature range of 400-450 degrees C was demonstrated to give high-quality optical waveguides which not only exhibit low propagation losses as low as 0.5 dB/cm at lambda =1.55 mu m but concomitantly high resistivity of >10/sup 4/ Omega cm. The refractive index of In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As was estimated to be 3.207+or-0.03 at lambda =1.55 mu m.<>     

Long wavelength MOCVD grown InGaAsN-GaAsN quantum well lasers emitting at 1.378-1.41 /spl mu/m

Low threshold InGaAsN QW lasers with lasing wavelength at 1.378 and 1.41 /spl mu/m were demonstrated by metal organic chemical vapour deposition (MOCVD). The threshold current densities are 563 and 1930 A/cm/sup 2/ for the 1.378 and 1.41 /spl mu/m emitting lasers, respectively. The significant improvement of device performance is believed due to utilisation of high temperature annealing and introduction of GaAsN barriers to suppress the resulting wavelength blue shift. A comparable characteristic temperature coefficient of the external differential quantum efficiency, T/sub 1/, is observed for the InGaAsN-GaAsN QW laser compared to similar InGaAsN/GaAs structures.     

Fabrication of high-performance InGaAsN ridge waveguide lasers with pulsed anodic oxidation

We have demonstrated high-performance InGaAsN triple-quantum-well ridge waveguide (RWG) lasers fabricated using pulsed anodic oxidation. The lowest threshold current density of 675 A/cm/sup 2/ was obtained from a P-side-down bonded InGaAsN laser, with cavity length of 1600 /spl mu/m and contact ridge width of 10 /spl mu/m. The emission wavelength is 1295.1 nm. The transparency current density from a batch of unbonded InGaAsN RWG lasers was 397 A/cm/sup 2/ (equivalent to 132 A/cm/sup 2/ per well). High characteristic temperature of 138 K was also achieved from the bonded 10/spl times/1600-/spl mu/m/sup 2/ InGaAsN laser.     

Aromatic polyureas: a new class of nonlinear optical polymer with large second-harmonic generation

The second-order nonlinear optical properties of aromatic polyureas are reported. From Maker fringe measurements, the nonlinear d/sub 33/ coefficient of poled polyurea films with and without pendant chromophores was found to be 20*10/sup -9/ esu and 12*10/sup -9/ esu, respectively, at 1.064 mu m. Aromatic polyurea having no pendant chromophores shows a cutoff wavelength of transmission at 307 nm which is the first example of organic NLO materials to be optically transparent at such low wavelengths.<>     

35 dB optical gain at 2.716 mu m in erbium doped ZBLAN fibre pumped at 0.642 mu m

An optical gain of 35 dB at 2.716 mu m signal wavelength has been measured in an erbium doped ZBLAN fibre. A pump-wavelength scanning determined the pump wavelength for maximum gain. This pump wavelength was found to be 0.642 mu m. The maximum absorption wavelength for this Er/sup 3+/ doped fibre is 0.649 mu m. It was deduced that the excited state absorption process improves the gain performance of such fibres at the signal wavelength considered.<>