Silica-based integrated optic Mach-Zehnder multi/demultiplexerfamily with channel spacing of 0.01-250 nm

A Mach-Zehnder (MZ) interferometer design is presented for application to wavelength-division multiplexed/frequency division multiplexed (WDM/FDM) systems. A variety of integrated-optic devices with low loss and low crosstalk, using silica-based waveguides, are demonstrated. MZ interferometers operate as multi/demultiplexers or frequency-selection switches. The channel spacing is determined by the waveguide arm length difference, and a spacing range of 1 GHz to 36 THz, corresponding to a wavelength spacing of 0.008-250 nm, is achieved. The devices for the WDM region have low fiber-to-fiber loss of 0.5 dB, and the devices for the FDM region have higher losses of 2-5 dB. Crosstalk of less than -15 dB was obtained for all the devices. A 5-GHz-spaced 16-channel frequency selection switch and a 10-GHz-spaced eight-channel multi/demultiplexer were also fabricated with a total loss of 5 dB and total crosstalk of -10 dB or less     

Fabrication of planar optical waveguides in LiB3O5 by 2 MeV He+ ion implantation

The fabrication of planar optical waveguides in LiB₃O ₅ is discussed. Using 2-MeV ⁴He⁺ implantation with a dose of 1.5×10¹⁶ ions/cm² at 300 K, the refractive indexes of a 0.2-μm-thick layer 5.1 μm below the crystal surface are reduced to form optical barrier guides. For this ion dose the maximum change from the bulk values of refractive index at a wavelength of 0.488 μm are 1.5%, 5.25%, and 4% for n_x, n_y, and n_z, respectively. The refractive indexes of the guiding region change by less than 0.02% from the bulk values. The dose dependence of the optical barrier height has been measured. A threshold ion dose of about 0.75×10¹⁶ ions/cm² is required to form a refractive index barrier and ion doses higher than about 2.5×10¹⁶ ions/cm². saturate the refractive index decrease. Waveguide propagation losses for annealed single energy implants of dose 1.5×10¹⁶ ions/cm² are dominated by tunneling and are estimated to be ~8.9 dB/cm for the z-cut waveguides used. Multiple energy implants broaden the optical barrier, and losses of <4 dB/cm have been observed     

Photorefractive effects in proton exchanged LiTaO3optical waveguides

A circuit model is proposed to describe photorefractive effects in LiNbO₃/LiTaO₃ channel waveguides at any intensity level. Capacitive charge storage at the waveguide boundaries is assumed to be provided by trapping states associated with photoconductivity. A consequence of this model is that photoconductive transients are independent of optical intensity at low intensity levels. Photovoltaic and photoconductive effects in proton exchange LiTaO₃ channel waveguides were experimentally investigated. Dark conductivities of 2×10^-15 to 2 ×10^-14(Ω-cm)^-1 were extrapolated from photoconductivities up to 2×10^-13 (Ω-cm)^-1 for power levels of 0.1 to 3 mW. Large DC voltage dependent effects on the conductivity were observed. Straight channel waveguides were observed to be free of photovoltaic effects for output power levels below 35-75 mW     

Ga2O3(Gd2O3)/InGaAsenhancement-mode n-channel MOSFETs

We have demonstrated the first Ga₂O₃(Gd₂O₃) insulated gate n-channel enhancement-mode In_0.53Ga_0.47As MOSFET's on InP semi-insulating substrate. Ga₂O₃(Gd₂ O₃) was electron beam deposited from a high purity single crystal Ga₅Gd₃O₁₂ source. The source and drain regions of the device were selectively implanted with Si to produce low resistance ohmic contacts. A 0.75-μm gate length device exhibits an extrinsic transconductance of 190 mS/mm, which is an order of magnitude improvement over previously reported enhancement-mode InGaAs MISFETs. The current gain cutoff frequency, f_t, and the maximum frequency of oscillation, f_max, of 7 and 10 GHz were obtained, respectively, for a 0.75×100 μm² gate dimension device at a gate voltage of 3 V and drain voltage of 2 V     

Guided wave modulators in Ti ion implanted LiNbO3waveguides

Electrooptic modulators in Ti-ion-implanted LiNbO₃ waveguides are discussed. Low loss (<1-dB/cm) planar and channel waveguides were fabricated and compared to indiffused waveguides. Higher Δn values are obtained, allowing smaller waveguide geometries and tighter mode confinement. Wavelengths of 0.85 and 1.3 μm are used. The small mode profiles resulting from the Ti doses up to 4×10¹⁷ Ti/cm² resulted in V-L products of 8.8 V-mm at 0.85 μm and 20 V-mm at 1.3 μm. These values are lower than any previously reported for a Mach-Zehnder modulator using a buffer layer. Comparison of diffused and implanted waveguide modulators indicated that modular efficiency can be optimized by electrode gap spacing and enhanced with smaller mode profiles achievable in implanted guides     

Fabrication of 2×2 crosspoint switches using a sputtered SiO2 intermixing technique

We report the fabrication of a 2×2 crosspoint switch, which monolithically integrates passive waveguides and electroabsorption modulators on one chip, using the sputtered SiO₂ technique for quantum-well intermixing. The static performance of the modulators has been tested, and a modulation depth of 25 dB has been obtained at a wavelength of 1.55 μm for an applied bias of 2 V     

Improved strained HEMT characteristics using double-heterojunctionIn0.65Ga0.35As/In0.52Al0.48As design

The DC and microwave properties of strained In_0.65Ga _0.35As/In₀₅₂Al_0.48As HEMTs (high electron-mobility transistors) with double-heterojunction design are presented. The high sheet carrier density and good carrier confinement give rise to excellent device performance with very low output conductance. For 1×150-μm² long-gate HEMTs, the measured cutoff frequency f_T and maximum frequency of oscillation f_max are as high as 37 and 66 GHz, respectively     

Improved gain performance in Yb3+-sensitized Er3+-doped alumina (Al2O3) channel opticalwaveguide amplifiers

Small-signal amplification in short, Yb³⁺-sensitized, Er³⁺-doped alumina (Al₂O₃) channel optical waveguides with high Er³⁺ concentrations is analyzed. Taking into account uniform up conversion, excited state absorption (ESA) from the Er³⁺ metastable level (⁴I_13/2 ), and Yb³⁺→Er³⁺ energy transfer by cross relaxation, the obtainable gain improvements compared to Yb³⁺ -free Er³⁺-doped Al₂O₃ optical waveguides are investigated. The amplifier model is based on propagation and population rate equations and is solved numerically by combining finite elements and the Runge-Kutta algorithm. The analysis predicts that 5-cm long Yb³⁺/Er³⁺ co-doped Al₂O ₃ waveguides show 13-dB net signal gain for 100 mW pump power at λ_p=980 nm     

Emission cross sections and spectroscopy of Ho3+ laserchannels in KGd(WO4)2 single crystal

The spectroscopic properties of Ho³⁺ laser channels in KGd(WO₄)₂ crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho³⁺ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω₂=15.35×10^-20 cm², Ω ₄=3.79×10^-20 cm², Ω₆ =1.69×10^-20 cm². The 7-300-K lifetimes obtained in diluted (8·10¹⁸ cm^-3) KGW:0.1% Ho samples are: τ(⁵F₃)≈0.9 μs, τ( ⁵S₂)=19-3.6 μs, and τ(⁵F₅ )≈1.1 μs. For Ho concentrations below 1.5×10²⁰ cm^-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τ_ph ^-1(0)=βexp(-αΔE), where β=1.4×10^-7 s^-1, and α=1.4×10³ cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho³⁺ emission cross section σ_EM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σ_EM values achieved for transitions to the ⁵I₈ level are ≈2×10^-20 cm² in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the ⁵I₇→⁵I₈ channel     

Measurement of the stimulated emission cross section for the 4F3/2-4I13/2transition of Nd3+ in YAlO3 crystal

A method for the simultaneous measurement of the stimulated emission cross section and fluorescence lifetime by studying the relation between laser parameters and the laser relaxation oscillation frequency is discussed. The stimulated emission cross section for the ⁴F_3/2-⁴I_13/2 transition of Nd³⁺ ion in YAP crystal was measured to be (22±1)×10^-20 cm²     

Ring resonators composed of GeO2-doped silica waveguides

Ring resonators composed of GeO₂-doped silica waveguides fabricated on silicon substrates by a flame hydrolysis deposition method are described. GeO₂-doped silica waveguides are developed to provide a lower propagation loss than that of TiO₂ -doped silica waveguides. Since the finesse and transmission at resonance is determined mainly by total loss in the ring, the loss characteristics of the fundamental components are investigated in detail. Experimental and theoretical investigations show that a finesse of the ring resonator for GeO₂-doped silica waveguides is about 2.7 times higher than that for TiO₂-doped silica waveguides with the same transmission at resonance     

Bi1.5Zn1.0 Nb1.5O7栅绝缘层的SiO2修饰对ZnO-TFTs性能的影响

具有高介电常数的栅绝缘层材料存在某种极化及耦合作用,使得ZnO-TFTs具有高的界面费米能级钉扎效应、大的电容耦合效应和低的载流子迁移率.为了解决这些问题,本文提出了一种使用SiO₂修饰的Bi_1.5Zn_1.0Nb_1.5O₇作为栅绝缘层的ZnO-TFTs结构,分析了SiO₂修饰对栅绝缘层和ZnO-TFTs性能的影响.结果表明,使用SiO₂修饰后,栅绝缘层和ZnO-TFTs的性能得到显著提高,使得ZnO-TFTs在下一代显示领域中具有非常广泛的应用前景.栅绝缘层的漏电流密度从4.5×10^-5A/cm²降低到7.7×10^-7A/cm²,粗糙度从4.52nm降低到3.74nm,ZnO-TFTs的亚阈值摆幅从10V/dec降低到2.81V/dec,界面态密度从8×10¹³cm^-2降低到9×10¹²cm^-2,迁移率从0.001cm²/（V·s）升高到0.159cm²/（V·s）.     

Refractory MoSi2and MoSi2/polysilicon bulk CMOS Circuits

Refractory MoSi2and MoSi2/polysilicon have been used to fabricate high-performance 3µm bulk CMOS circuits. Thirty-nine stage ring oscillators, with a fan-in and fan-out of 1, exhibit a switching delay/stage of 1.2 to 1.4ns, and a power-delay product of 0.22 to 0.25pJ at a supply voltage of 5V. The power-delay product ranges from 40fJ for a delay of 9ns to 1pJ for a delay of 0.6ns. Self-checking pattern generator circuits implemented with the same technology show an operating frequency as high as 80 MHz, which corresponds to approximate in-circuit delays of 1.2ns/stage.     

High-frequency submicrometerAl0.48In0.52As/In0.53Ga0.47As heterostructure bipolar transistors

The high speed scaling of an Al_0.48In_0.52As/In_0.53Ga_0.47 As submicrometer heterostructure bipolar transistor (HBT) is presented. Transistors with emitter dimensions of 0.5×11 and 3.5×3.5 μm² exhibit unity current-gain cutoff frequencies of 63 and 70 GHz, respectively. Emitter current density greater than 3.3×10⁵ A/cm² is demonstrated in a submicrometer AlInAs/InGaAs HBT. The analysis shows that the device speed is limited by the parasitic collector charging time     

KrF excimer laser annealed TFT with very high field-effect mobilityof 329 cm2/V-s

A thin-film transistor (TFT) with a maximum field-effect mobility of 320 cm²/V-s, an on/off current ratio of 7.6×10⁷ , a threshold voltage of 6.7 V and a subthreshold slope of 0.37 V/decade was fabricated by using pulse laser annealing processes. Amorphous silicon films (a-Si:H) with a very low impurity concentration of 4×10¹⁸ cm^-3 for oxygen, 1.5×10¹⁸ cm^-3 for carbon, and 2×10¹⁷ cm^-3 for nitrogen were deposited by a plasma chemical vapor deposition (CVD) method and annealed by KrF excimer laser (wavelength of 248 nm). The Raman spectroscopy technique was a useful tool for optimizing laser annealing conditions. Experimental results show that two factors are very important for fabricating very-high mobility TFTs: (1) utilizing high-purity as-deposited a-Si:H film; and (2) performing whole laser annealing processes sequentially in a vacuum container and optimizing illumination conditions     

Extremely large band gap shifts for MQW structures by selectiveepitaxy on SiO2 masked substrates

The authors investigate selective epitaxy through SiO₂ masks of varied geometry with the goal of making planar photonic integrated circuits. The InGaAs/InP, InGaAsP/InP, and InGaAs/InGaAsP MQW material systems are studied with atmospheric and 100-torr MOVPE. Extremely large bandgap shifts (136 meV) can be achieved, more than enough to allow construction of lasers, modulators, and low-loss waveguides in a single plane     

Silicon bipolar chipset for SONET/SDH 10 Gb/s fiber-opticcommunication links

High-speed multiplexers, demultiplexers, frequency dividers, mixers, and amplifiers are key electronic components in high-speed fiber-optic communications systems such as SONET/SDH. In this paper, we present several important digital and analog integrated circuits (IC) which have been developed for use in SONET/SDH 10 Gb/s optical communication links. The circuits have been fabricated in MOSAIC 5E, an advanced silicon bipolar technology (f_T=26 GHz). The resulting chipset which amounts to a total of 10 IC's consists of multiplexers, demultiplexers, a regenerative frequency divider (2:1), a dual output limiting amplifier, and two different types of mixers for clock extraction. Specifically, the design and performance of these IC's and a hybrid clock recovery module are discussed. The high performance and potential low cost of this research chipset show that advanced silicon bipolar circuit technology can play an important role in future multigigabit fiber-optic communication systems     

Fabrication of high-performance AlxGa1-xAs/InyGa1-yAs/GaAs resonant tunneling diodes using amicrowave-compatible technology

A microwave-compatible process for fabricating planar integrated resonant tunneling diodes (RTDs) is described. High-performance RTDs have been fabricated using Al_xGa_1-xAs/In_y Ga_1-yAs/GaAs strained layers. Peak-to-valley current ratios (PVRs) of 4.8:1 with simultaneous peak current densities of 4×10⁴ A/cm² have been achieved at room temperature for diodes of area 9 μm². Accurate measurements of reflection gain versus frequency between 1.5 and 26.5 GHz in the negative differential region indicate that the present technology is promising for millimeter-wave integrated circuits including self-oscillating mixers, frequency multipliers, and detectors     

Erase/write cycle tests of n-MOSFETs with Si-implantedgate-SiO2

To discuss the applicability of a MOSFET with Si-implanted gate-SiO₂ of 50 nm thickness to a non volatile random access memory (NVRAM) operating more than 3.3×10¹⁵ erase/write (E/W) cycles, E/W-cycle tests were performed up to 10¹¹ cycles by measuring the hysteresis curve observed in a source follower MOSFET in which a sine-wave voltage of 100 kHz was supplied to the gate. Degradations in the threshold-voltage window of 15 V and gain factor were scarcely observed in a MOSFET with Si-implantation at 50 keV/1×10¹⁶ cm^-2 at a gate voltage of ±40 V. Those degradations observed in a MOSFET with 25 keV/3×10¹⁶ cm^-2 were improved by lowering the gate voltage from ±40 V to ±30 V in sacrificing the smaller threshold-voltage window from 20 to 8.5 V     

Ultrafast time-division demultiplexer based on electrooptic on/offgates

Electrooptic on/off gate-based demultiplexers for high-bit-rate optical transmission systems are reported. The electrooptic demultiplexing of a TDM 49.6 Gb/s fixed pattern data stream is demonstrated, using two cascaded Ti:LiNbO₃ electroabsorptive multi-quantum-well intensity modulators driven at 6.2 GHz. Error-free 10 Gb/s demultiplexing to 5 Gb/s is achieved using cascaded Mach-Zehnder (MZ) modulators driven at 1.25 GHz. The power penalty due to the interchannel crosstalk is 0.3 dB at the bit error rate of 10^-9