Photonic generation of continuous THz wave using uni-traveling-carrier photodiode

A uni-traveling-carrier photodiode (UTC-PD) is monolithically integrated with a wideband log-periodic toothed antenna for generating millimeter and submillimeter waves at frequencies of up to terahertz range. A module with a quasi-optical output port fabricated for practical use operates up to 1.5 THz and generates an output power of 2.3 /spl mu/W at 1.04 THz with good linearity. The output power level and the operation frequency are records for wideband PD modules operating at 1.55 /spl mu/m. An investigation of the operational characteristics of the UTC-PD reveals that the effective use of the electron-velocity overshoot in the junction depletion layer is important for maximizing the output power in the terahertz range.     

Analysis of a PIN photodiode with integrated waveguide

The absorption coefficient of an InGaAs PIN photodiode integrated with an InGaAsP-InP waveguide is analysed by means of the mode-matching technique. The results compare excellently to published data for ? = 1.3 ?m. It is shown that by an optimised device structure the absorption coefficient can be increased to about 0.15 dB/?m, enabling reduced detector length and smaller capacitance.     

Edge-coupled InGaAs PIN photodiode with a light funnel waveguide

We have successfully fabricated InGaAs edge-coupled photodiodes (EC-PDs) with a light funnel integrated (LIFI) in front of the coupling aperture, called LIFI EC-PD, based on the self-terminated oxide polish (STOP), the crystallographic slope etching of InP, and the self-aligned diffusion (SAD) techniques. The LIFI EC-PD presents not only a lower dark current density (/spl sim/ 4.4 mA/cm/sup 2/) but also a higher responsivity (/spl sim/ 0.4 A/W) than that of the mesa EC-PD (27 mA/cm/sup 2/ and 0.26 A/W, respectively). Furthermore, the thick oxide film serves as the funnel in front of active-region aperture to enhance the coupling efficiency and to lower the bonding pad capacitance down to 50 fF. The lowered bonding pad capacitance can be beneficial in designing a device with a higher transit-time-limited frequency response of beyond 30 GHz. The LIFI EC-PD with a 1-/spl mu/m thick absorption layer exhibits a 3-dB bandwidth of 20 GHz and a responsivity of /spl sim/ 0.4 A/W.     

An 80-Gb/s optoelectronic delayed flip-flop IC using resonanttunneling diodes and uni-traveling-carrier photodiode

This paper describes an 80-Gb/s optoelectronic delayed flip-flop (D-FF) IC that uses resonant tunneling diodes (RTDs) and a uni-traveling-carrier photodiode (UTC-PD). A circuit design that considers the AC currents passing through RTDs and UTC-PD is key to boosting circuit operation speed. A monolithically fabricated IC operated at 80 Gb/s with a low power dissipation of 7.68 mW. The operation speed of 80 Gb/s is the highest among all reported flip-flops. To clarify the maximum operation speed, we analyze the factors limiting circuit speed. Although the bandwidth of UTC-PD limits the maximum speed of operation to 80 Gb/s at present, the circuit has the potential to offer 100-Gb/s-class operation     

W波段反对称渐变探针过渡转换的设计

介绍了一种反对称渐变波导微带探针过渡结构,采用高频仿真软件HFSS仿真分析了这个波导微带过渡结构在W频段的特性,并对影响过渡性能的几个因素进行了敏感性分析,得出了可供工程应用参考的设计曲线。在全波导带宽内,实现了插入损耗小于0.088 dB,回波损耗大于27 dB。该结构具有宽频带、结构简单和易加工等优点,可广泛用于毫米波固态电路系统中。     

15 Gbit/s optical receiver using waveguide pin photodiode

The authors report the first optical receiver to use a waveguide pin photodiode as a high-power and high-speed photodiode. Its measured receiver sensitivity of 15 Gbit/s confirms that waveguide pin photodiodes have high-speed potential and flat frequency response under high input powers beyond +10 dBm     

W-band InP HEMT MMICs using finite-ground coplanar waveguide(FGCPW) design

In this paper, we report on the development of W-band monolithic microwave integrated circuit (MMIC) power amplifiers using 0.1-μm AlInAs/GaInAs/InP high electron mobility transistor (HEMT) technology and finite-ground coplanar waveguide (FGCPW) designs. In the device modeling, the Angelov nonlinear HEMT model was employed to predict the large signal performance of the device, and the results were validated by using state-of-the-art vector load-pull measurements. A two-stage single-ended W-band FGCPW MMIC using a 150-μm-wide HEMT as the driver and a 250-μm-wide HEMT for the output stage was designed, fabricated, and tested. The MMIC amplifier demonstrates a maximum output power of 18.6 dBm with 18.2% power-added efficiency and 10.6 dB associated gain at 94 GHz. This result is the best output power to date reported from an InP-based MMIC using FGCPW design at this frequency     

Analytical modeling of a high-performance near-ballistic uni-traveling-carrier photodiode at a 1.55-/spl mu/m wavelength

In this letter, we developed an analytical equivalent circuit model, which includes the resistance-capacitance-delay time and carrier transport time, to investigate the distinct dynamic performance of the near-ballistic uni-traveling-carrier photodiode (NBUTC-PD). This device, in which the structure of the collector of the UTC-PD is modified, can achieve excellent performance at a 1.55-/spl mu/m wavelength. According to the measured frequency responses of the scattering (S) parameters of NBUTC-PD and detailed device-modeling, the observed significant reduction of the device capacitance and the enhancement of the net optical-to-electrical bandwidth under high-power operation can be attributed to the unique near-ballistic-transport property of the photogenerated electron, which has never been observed in the traditional high-speed high-power photodiode.     

A planar slab-waveguide photodiode with a pseudowindow region infront of the waveguide

A planar waveguide photodiode having a selectively diffused p-n-junction with a simple pseudowindow region has been developed for access network applications. By forming the p-n-junction away from the input facet of the diode, the input facet is kept in neutral under the reverse-bias condition. We expect the facet degradation to be significantly suppressed in this structure. An extremely low dark current of less than 3 pA and sufficient bandwidth of over 4 GHz were confirmed     

波导CO2激光器输出镜的研究

通过实验，证明了高功率CO2波导激光器输出镜使用砷化镓是必须的，而锗只适用于低功率波导CO2激光器。讨论了透过率与输出功率的关系和谐振腔材料对输出     

50-GHz passively mode-locked surface-emitting semiconductor laser with 100-mW average output power

We have developed a passively mode-locked optically-pumped vertical-external-cavity surface-emitting semiconductor laser (VECSEL) which delivers up to 100 mW of average output power at a repetition rate of 50 GHz in nearly transform-limited 3.3-ps pulses at a wavelength around 960 nm. The high-repetition-rate passive mode locking was achieved with a low-saturation-fluence semiconductor saturable absorber mirror (SESAM) incorporating a single layer of quantum-dots. The output power within a nearly diffraction-limited beam was maximized using a gain structure with a low thermal impedance soldered to a diamond heat spreader. In addition, we systematically optimized the laser resonator to accommodate for the strong thermal lens caused by the optical pumping. We measured the thermal lens dioptric power and present a numerical model which is in good agreement with the measurements and is useful for optimizing resonator designs. The experimental setup is very versatile and its design and construction are discussed in detail.     

2.05-μm wavelength InGaAs-InGaAs distributed-feedbackmultiquantum-well lasers with 10-mW output power

Single-mode operation beyond 2.05-μm wavelength has been achieved in InGaAs-InGaAs distributed-feedback (DFB) laser with four quantum wells. The continuous-wave output power is 10.5 mW at a drive current of 200 mA and 25°C, The tuning range of the wavelength is between 2.051-2.056 μm with a temperature tuning rate of +0.125 nm/°C     

A 110-dB-THD, 18-mW DAC using sampling of the output and feedbackto reduce distortion

A one-bit digital-to-analog converter architecture is presented that reduces distortion through the use of feedback. The only critical circuit in this architecture is identical to the first integrator of a ΔΣ analog-to-digital converter. All other circuits in the system are embedded in the feedback loop, which reduces the effects of their nonidealities. Special attention was given to the distortion arising from the discrete-time to continuous-time interface. The feedback loop is a conditionally stable system using multipath feedforward compensation. A total harmonic distortion of -110 dB is achieved. The signal-to-noise ratio is 114 dB in 400 Hz, and out-of-band noise is below -50 dB using only one external component. The power consumption is 18 mW from a 5-V supply. Die area is 3.6 mm² in 0.6-μm DPTM-CMOS technology     

Some aspects of bias current tuning of W-band IMPATT diodes mounted in a reduced-height waveguide circuit

The bias current tuning of W-band IMPATTs in reduced-height waveguide circuits have been discussed in details. The measured tuning response can be increasing, decreasing or practically insensitive with bias current depending on the device and circuit parameters. The observed results are explaine with a simple device-circuit interaction model.     

A 0.25-μm gate-length pseudomorphic HFET with 32-mW output powerat 94 GHz

The 94-GHz power performance of a 0.25×75-μm doped-channel pseudomorphic heterostructure FET (HFET) is reported. A maximum output power of 32 mW, corresponding to a power density of 0.43 W/mm, was obtained with 15% power-added efficiency and 3.0 dB gain     

A GaAs Schottky-barrier photodiode with high quantumefficiency-bandwidth product using a multilayer reflector

A GaAs Schottky-barrier with high quantum efficiency-bandwidth product has been developed by using a GaAs/Al_0.25Ga_0.75 As multilayer reflector. The multilayer reflector structure wa designed by using the scattering matrix method. By growing four pairs of Al_0.25Ga_0.75As (825 Å)/GaAs (330 Å) multilayer reflectors between the undoped GaAs active layer and the buffer layer, a responsivity of 0.6 A/W at λ=0.84 μm was obtained for this device. This represents a 30% improvement over the device without a multilayer reflector. The response speed of the photodiode was measured by the impulse response method, and the results yielded a rise time of 38.45 ps, corresponding to a bandwidth of 9 GHz for this detector     

Measurements of a fabricated micro mirror using a lateral-effectposition-sensitive photodiode

The characteristics of a fabricated micro mirror were determined using an optical measurement system. The system consisted of a helium-neon laser, a p-i-n lateral-effect photodiode, and other fundamental optical elements. For testing, we used a micro mirror array (1×4) in which each mirror was composed of a mirror plate, two torsional flexure hinges, two address electrodes, and two support posts. A mirror plate was designed to a size of 100×110×1.5 μm ³ and the hinge size was 20 μm long, 5 μm wide, and 0.5 μm thick. The micro mirror array was fabricated using micromachining technology and a lithography-galvanoformung-abformung-like process using nickel electroplating. The variation in the mirror's deflection angle with applied voltage was measured as a static characteristic. The downward threshold voltage of the 0.5-μm thick hinge was 48 V. The step response time, as a dynamic characteristic, was 21.8 μs when a 64 V step voltage higher than the downward threshold voltage was applied to an address electrode. The lifetime of the fabricated micro mirror was tested for both unidirectional and bidirectional operation     

Short-cavity distributed Bragg reflector laser with an integrated tapered output waveguide

A distributed Bragg reflector strained-layer multiple-quantum-well laser at 1.5- mu m wavelength with an integrated tapered waveguide beam expander is discussed. The far-field FWHMs in the lateral and vertical directions are 10 and 15 degrees , respectively. A quantum efficiency of 17% out the tapered facet was measured with a corresponding threshold current of 28 mA. The alignment tolerances for coupling into a cleaved single-mode fiber are 9.5 and 7.5 mu m FWHM in the lateral and vertical directions, respectively. A 3-dB improvement for single-mode fiber coupling using a SELFOC lens was obtained.<>     

Analysis of an N-way radial cavity divider with a coaxial centralport and waveguide output ports

A field matching technique is used to analyze an N-way divider which includes a radial cavity with a coaxial central port and H-plane coupled rectangular waveguide output ports. Dielectric coated and disc ended probes at the central port are considered. The analysis is divided into two parts. Part one is associated with the modeling of the central port and part two is concerned with the modeling of the waveguide peripheral ports. The analysis is simplified by assuming that the interaction between the central port and the peripheral ports is by means of axially symmetric radial waves which are uniform with cavity's height. Based on this analysis, algorithms are developed for calculating the scattering parameters of this structure using a PC. These algorithms show good agreement when tested against a finite element package (HFSS) and against measurements     

Polarization-independent waveguide modulator using a novel quantumwell with mass-dependent width

We propose a novel quantum well (QW) structure with two or four thin barriers inserted in which effective width of the well is mass-dependent. It is very useful for polarization-independent optical modulation. Incorporation of tensile strain is also discussed for further improvement of the polarization insensitivity. Fabrication of a modulator with lattice-matched QW's results in 6-V switching voltage with more than -10-dB extinction (--30 dB maximum) for both TE and TM modes over 29-nm wavelength range. Compared with the quasiparabolic QW, this new quantum well has better fabrication tolerance, wider wavelength range of operation, and higher yield