Dual-wavelength laser source monolithically integrated with Y-junction coupler and isolator using quantum-well intermixing

A dual-wavelength laser source monolithically integrated with an isolator and a Y-junction coupler is fabricated by using a new quantum-well intermixing technique. The technique employs a buried Ge layer between the sample surface and the spin-on silica film to control the bandgap tuning in selective areas across a wafer. The integrated isolator can avoid the crosstalk between the two channels of the device. Two distinct lasing wavelengths of 950 and 969 nm are coupled into one single output port through the transparent Y-junction coupler. The two channels have similar threshold current and slope efficiency.     

Tunable sampled-grating DBR lasers using quantum-well intermixing

Widely tunable lasers are key components for wavelength division multiplexing fiber optic networks. They reduce cost in sparing, enable dynamic networking applications, and present opportunities for future monolithically integrated wavelength division multiplexing components. The sampled-grating distributed Bragg reflector (SGDBR) laser is ideal for these purposes. The authors present a centered quantum-well SGDBR laser which uses quantum-well intermixing in order to improve device characteristics over previous designs. The mode overlap is improved by 50% over the offset quantum-well design, improving the modal gain. Current injection tuning in the intermixed material is demonstrated for the first time; the maximum modal group index change was measured to be 1%.     

Monolithically integrated optical gate 2 × 2 matrix switch using GaAs/AlGaAs multiple quantum well structure

A 2 × 2 optical matrix switch, monolithically integrating multiple-quantum-well-gate and optical circuits fabricated by the reactive-ion-beam etching method, is described. The switch size is small, 3 mm × 1.2 mm. Low crosstalk of 20 dB at 12 V is achieved.     

Single-mode guided-wave optical gate matrix switch using Mach-Zehnder interferometer gates

A 4 × 4 optical gate matrix switch is fabricated from high-silica single-mode guided-wave optical circuits. Mach-Zehnder interferometer circuits operated by electrical heating are used as optical gates. The switch has a 400 Mbit/s switching bandwidth.     

Modeling of optical gain properties of multiple cationsInGaAs-InAlAs quantum-well intermixing

Multiple cations intermixing in an In_0.53Ga_0.47 As-In_0.52Al_0.48As quantum-well (QW) structure with 60-Å well width is being studied based on the expanded form of Fick's second law. Interdiffusion of the indium sublattice can result in a maximum compressive strain of 0.64% when annealing time reaches 3 h at 812°C. For a small interdiffusion, i.e., 1-1.5 h, the subband separation between the lowest heavy and light hole states is at its greatest. This has a major contribution to the modified band structure and averaged density of states which can result in an enhanced optical gain up to 40%. This initial stage of intermixing provides the best lasing performance. For large interdiffusion, i.e., up to 6 h, a large blue shift of the peak gain from 0.842 eV (λ=1.47 μm) to 1.016 eV (λ=1.22 μm) is obtained, thus giving a high tunability of the lasing wavelength     

Improvements in mode-locked semiconductor diode lasers using monolithically integrated passive waveguides made by quantum-well intermixing

By using the technique of quantum-well intermixing (QWI), monolithically integrated passive, and active waveguides can be fabricated. It is shown that mode-locked extended cavity semiconductor lasers with integrated low-loss passive waveguides display superior performance to devices in which the entire waveguide is active: the threshold current is a factor of 3-5 lower, the pulsewidth is reduced from 10.2 ps in the all active laser to 3.5 ps in the extended cavity device and there is a decrease in the free-running jitter level from 15 to 6 ps (10 kHz-10 MHz).     

Dispersion and modulation of the linear optical properties of GaAs-AlAs superlattice waveguides using quantum-well intermixing

We report on the large modulation of the optical properties of a 14:14 monolayer GaAs-AlAs superlattice waveguide following quantum-well intermixing. Low-temperature photoluminescence measurements illustrate a large 169-meV differential blue-shift obtained between the disordering-suppressed and disordering-enhanced materials. Effective index measurements are presented as a function of polarization, for both the as-grown and disordered material for near-bandedge and half-bandedge wavelengths, which is the wavelength range 775-1550 nm. The largest effective refractive index shift observed was 9/spl times/10/sup -2/ which exceeds that previously reported for disordered AlGaAs ternary multilayer structures, and illustrates the potential of the superlattice for the fabrication of etch-free, planar optical components with large index contrast.     

Multiple-wavelength integration in InGaAs-InGaAsP structures using pulsed laser irradiation-induced quantum-well intermixing

In this paper, we present the characteristics of a quantum-well intermixing technique using pulsed-photoabsorption-induced disordering. Photoluminescence, micro-Raman spectroscopy, and transmission electron microscopy were used to characterize the process. Using this technique, a differential wavelength shift between the intermixed and nonintermixed regions of over 160 nm has been observed from InGaAs-InGaAsP heterostructures. It was found from the micro-Raman measurements that a spatial resolution of better than 2.5 /spl mu/m can be achieved. A theoretical model has been developed to estimate the spatial resolution limit. Theoretical analysis has also been performed to investigate the effect of laser irradiation on the degree of intermixing in InGaAs-InGaAsP structures. To verify the capability of this process in monolithic photonic integration, high-quality bandgap tuned lasers, two-section extended cavity lasers, and multiple-wavelength laser chips have been fabricated.     

8/spl times/8 optical switch matrix using generalized Mach-Zehnder interferometers

We report an 8/spl times/8 strictly nonblocking optical cross connect (OXC) using multimode imaging (MMI)-based generalized Mach-Zehnder (MZ) interferometers realized in the silica-on-silicon planar waveguide system. Employing a router-selector architecture, this MMI-MZ OXC design results in a significantly smaller device than conventional directional-coupler based implementations. An average insertion loss of 6 dB and crosstalk of -34 dB, is demonstrated for the 8/spl times/8 OXC.     

Monolithically integrated optical channel monitor for DWDM transmission systems

The design, fabrication, and performance of an InP-based monolithically integrated optical power monitor are presented. It contains 44 wavelength channels separated by 100 GHz and demonstrates record small footprint size. The device's major components, which include the echelle diffractive grating demultiplexer, passive waveguide circuitry and single-mode vertically integrated waveguide PIN photodetectors, are characterized and discussed as generic building blocks of InP-based planar lightwave technology for DWDM.     

1.55 micrometer ridge DFB laser integrated with a buried-ridge-stripe dual-core spot-size converter by quantum-well intermixing

A ridge distributed feedback laser monolithically integrated with a buried-ridge-stripe spot-size converter operating at 1.55 micrometre wavelength was successfully fabricated by means of low-energy ion implantation quantum-well intermixing and dual-core technologies. The passive waveguide was optically combined with a laterally exponentially tapered active core to control the mode size. The devices emit in a single transverse and single longitudinal mode with a sidemode suppression ratio of 38.0 dB. The threshold current was 25 mA. The beam divergence angles in the horizontal and vertical directions were as small as 8.0 degree X 12.6 degree, respectively, resulting in 3.0-dB coupling loss with a cleaved single-mode optical fiber.     

Monolithically integrated optical differential amplifiers forapplications in smart pixel arrays

The design, fabrication, and characterization of monolithically integrated single- and dual-stage cascadable optical differential amplifiers (ODAs) are presented. The circuits are realized with photodiodes (PDs), metal-semiconductor field-effect transistors (MESFETs) and light-emitting diodes (LEDs) in the GaAs-AlGaAs system. They are fabricated with a process which uses trench technology for the separation of the devices. The single-stage switching energy of 2.5 pJ is reduced to 0.4 pJ by the addition of a second stage, thereby increasing the bandwidth from 2 to 12 MHz., The output power is 30 μW, and the measured contrast ratio is approximately 1000. Switching is possible over an input power range of more than 5 decades, with a lower limit of 15 pW. We measure an optical open-loop gain of 2·10⁶ and a power dissipation of 15-20 mW     

Monolithically integrated high-power broad-band RF switch based on III-N insulated gate transistors

We report on the high-performance monolithically integrated RF switch based on metal-oxide-semiconductor III-N heterostructure field-effect transistors (MOSHFETs). The radio frequency (RF) switch microwave monolithic integrated circuit (MMIC) consists of three submicron-gate MOSHFETs connected into /spl pi/-type configuration. In the 0-10 GHz frequency range, the insertion loss is less than 1dB and the isolation is better than 20 dB. The switching powers well exceed 20 W per 1mm of the active element width. The high performance parameters of the switch are achieved due to unique properties of III-nitride MOSHFET, which combines a low channel resistance and high breakdown voltage features of AlGaN/GaN HFETs and extremely low gate leakage currents, large gate voltage swing and low gate capacitance specific to insulated gate design. The combination of these parameters makes MOSHFETs excellent candidates for high-power switching. The experimental data obtained from the RF switch are in close agreement with the results of simulations.     

Study of all-optical XOR using Mach-Zehnder Interferometer and differential scheme

All-optical XOR functionality has been demonstrated experimentally using an integrated SOA-based Mach-Zehnder interferometer (SOA-MZI) at 20 and 40 Gb/s. The performance of the XOR results has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the carrier lifetime in the SOA. In order to solve the limitations imposed by carrier lifetime, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to >100 Gb/s.     

Integration of high-gain and high-saturation-power active regions using quantum-well intermixing and offset-quantum-well regrowth

A novel structure and method for fabricating regions of high and low modal gain on the same chip are reported, which enable diode lasers with maximum efficiency to be monolithically integrated with multiple-section semiconductor optical amplifiers having both high gain and high saturation power. This method uses quantum-well intermixing and an offset-quantum-well regrowth to achieve regions with high and low optical confinement. Fabry-Perot broad-area lasers were used to characterise the material in both regions.     

Monolithically integrated 4*4 InGaAsP/InP laser amplifier gate switch arrays

Monolithically integrated 4*4 semiconductor laser amplifier gate switch arrays comprising 24 integrated laser amplifiers have been fabricated and evaluated. Net positive optical gain between fibres, high extinction ratio, and low crosstalk are reported.<>     

Monolithically integrated long wavelength optical receiver OEICs using InAlAs/InGaAs heterojunction MESFETs (HFETs)

Monolithic optical receiver OEICs have been successfully fabricated on 2" diameter InP substrates by integrating an InGaAs pin photodetector with a simple InAlAs/InGaAs heterojunction MESFET (HFET) structure. Transimpedance receivers based on 1.5 mu m gate length FETs exhibited 3.5 GHz bandwidth and 19.9 pA/ square root (Hz) averaged noise current. Circuit functional yield as high as 67% has been achieved.<>     

Experimental and theoretical analysis of argon plasma-enhanced quantum-well intermixing

Plasma-enhanced quantum-well intermixing (QWI) has been developed for tuning the bandgap of InGaAs-InP material using an inductively coupled plasma system. The application of inductively coupled plasma enhances the interdiffusion of point defects resulting in a higher degree of intermixing. Based on a semi-empirical model of QW interdiffusion, the bandgap blue-shift with respect to the plasma exposure time and inductively coupled plasma energy has been analyzed. The theoretical results appear to be in good agreement with the experimental data of the intermixed samples. The model serves as a good simulation tool to explain the intermixing mechanism and further to optimize the intermixing process for the fabrication of the photonic integrated circuits.     

GeSi/Si Mach-Zehnder干涉型调制器的研制

基于ＧｅＳｉ合金的等离子体色散效应,研制了一种Ｍａｃｈ－Ｚｅｈｎｄｅｒ干涉型调制器,通过对其损耗和调制特征的测试得到：调制器对１．３μｍ光的插入损耗为６．５ｄＢ,最大调制深度达８５％,相应的π相移调制民压为０．９Ｖ,关断电流和调制区的注入电流密度分别为４０ｍＡ和０．９７ｋＡ／ｃｍ＾２。     

Integrated astable optical multivibrator using Mach-Zehnder interferometric optical switches

An integrated astable optical multivibrator has been analysed and demonstrated experimentally for the first time using a couple of Mach-Zehnder interferometric optical switches with crossed and straight electronic feedback. Fairly good agreement is found between experimental and analytical results.