Low-loss single-mode GaAs/AlGaAs miniature optical waveguides withstraight and bending structures

Low-loss single-mode GaAs/AlGaAs miniature optical waveguides fabricated for use in monolithically integrated optical circuits are discussed. The propagation characteristics of these waveguides with straight and S-bending structures have been investigated at wavelengths of 1.30 and 1.55 μm. The lowest propagation losses are estimated to be 0.58 dB/cm and 0.69 dB/cm at wavelengths of 1.30 and 1.55 μm, respectively. The total loss of an S-bending waveguide with a curvature radius of 2 mm and with a lateral displacement of 200 μm was 0.61 dB and 0.46 dB at wavelengths of 1.30 and 1.55 μm. The fabricated single-mode strip-loaded waveguides proved to be suitable for application of the semiconductor waveguide into monolithically integrated optical circuits     

Compact mode expanders using resonant coupling between a taperedactive region and an underlying coupling waveguide

A novel technique for enhanced laser-fiber coupling, based on resonant power coupling between a tapered active waveguide and an underlying coupling waveguide, is presented. Spot-sizes are transformed from 2.0×1.1 μm in the active region to 6.0×3.1 μm in the coupling waveguide, over a length of 200 μm, with a mode transformation loss of only 0.36 dB. Butt-coupling efficiencies of 55% (2.6 dB loss) are estimated to standard cleaved single-mode fibers at 1.55 μm. The proposed device requires a single epitaxial growth and conventional processing techniques, making it amenable for low-cost manufacturing     

A -80 dB THD, 4 Vpp switched capacitor filter for 1.5 Vbattery-operated systems

A fully differential fifth-order SC filter that can operate from power supplies as low as 1.5 V featuring a -80 dB THD up to 4 V_pp output voltage is presented. A measured p-weighted noise of 120 μV_rms leads to a dynamic range of 81.5 dB. This circuit is used as reconstruction filter for a low voltage 14-b DAC. The very low voltage operation has been possible by integrating a regulated voltage-multiplier on the same chip. The filter active area is 0.54 mm ² in a 0.8 μm CMOS technology. Typical power consumption is 0.8 mW at 1.5 V supply     

Laminated polarizers exhibiting high performance over a wide rangeof wavelength

A laminated polarizer exhibiting high performance over a wide range of wavelengths has been fabricated for the first time. The polarizer consists of alternate layers of laminated silica film and metal-included semiconductor ultra-thin film as the transparent and absorptive layers, respectively. Extinction ratios of greater than 50 dB with insertion losses of less than 0.4 dB have been obtained over the wavelength range of 0.8-1.55 μm. At the wavelength 0.98 μm where previously no viable laminated polarizer had been available, the extinction ratio is as high as greater than 60 dB and the insertion loss less than 0.3 dB     

Fused taper/filter hybrid single-mode wavelength divisionmulti/demultiplexer

A low loss and low crosstalk single-mode wavelength division multi/demultiplexer was successfully fabricated by embedding an interference filter in each output arm of a fused taper coupler. The insertion loss was around 1.5 dB at the wavelengths of 1.3 μm and 1.55 μm, and both near-end and far-end crosstalks were less than -50 dB     

Polarization- and wavelength-insensitive guided-wave optical switchwith semiconductor Y junction

A polarization- and wavelength-insensitive semiconductor guided-wave optical switch with a Y junction is proposed. The switch exhibits a digital response with respect to current, allowing its use as a wavelength-insensitive 1×2 optical switch. The switching characteristics are analyzed by using the beam propagation method, and a design example is given. The polarization- and wavelength-insensitive switching operation has been confirmed with a fabricated GaAs/GaAlAs switch at wavelengths of 1.3 and 1.55 μm, and the on/off ratio exceeded 20 dB at an injection current of 250 mA at these wavelengths     

An 8-channel digitally tunable transmitter with electroabsorptionmodulated output by selective-area epitaxy

We demonstrate an 8-frequency digitally tunable laser based on a waveguide grating router with an electroabsorption modulated output. The laser wavelengths range from 1.567 to 1.580 μm with channel spacings of 200 GHz (1.6 nm). The modulator extinction is -10 dB/VN with a -5-V bias. A unique output coupler design delivers an ASE noise suppression of -55 dB/Å     

Reflection-type optical waveguide switch with bow-tie electrode

Based on the total internal reflection and the plasma dispersion effect of SiGe alloy, an intersectional rib optical waveguide switch with bow-tie electrode has been proposed and fabricated for operating wavelengths of 1.3 and 1.55 μm. The thickness of the SiGe layer is 2.6 μm and the width is 9 μm. The branch angle of the switch is 2° and the bow-tie angle is 1.5°. The crosstalks are -19.6 dB for 1.3 μm and -21.8 dB for 1.55 μm. At both wavelengths, the extinction ratio is larger than 38.5 dB and the insertion loss is less than 1.70 dB. The switching time is about 180 ns     

A 3.3-V 800-nVrms noise, gain-programmable CMOSmicrophone preamplifier design using yield modeling technique

A 3.3-V CMOS low-noise gain-programmable microphone amplifier with a high-impedance balanced input is presented. The preamplifier allows gains from 20 to 35 dB to be set by software control in 1-dB steps with 0.05-dB accuracy. Typical measured V_OS is 0.8 mV, V_OS drift is 1 μV/C, input-referred p-weighted noise is 0.8 μV _rms and total harmonic distortion (THD) is -70 dB. The active area is about 350 mils², and power consumption is 1.7 mW at 3.3-V supply and 2.9 mW at 5-V supply. These results have been obtained through an intensive use of the yield modeling technique for yield-performance optimization during the design phase, and by applying a common-centroid cross-coupled strategy to the layout of all the ideally matched MOS transistors in the input stage     

Stable single-mode operation of an 850-nm VCSEL with a higher ordermode absorber formed by shallow Zn diffusion

We report that an 850-nm vertical-cavity surface-emitting laser with a planar higher order mode absorber, formed by shallow Zn diffusion (<0.3 μm), operated at stable single-mode over the entire drive current range. A device with a 5×5 μm² absorber aperture and a 5×5 μm² oxide confined active region showed a ~0.8 mA threshold and a mode suppression ratio of 40 dB. The modeling indicates that the higher order modes will be suppressed strongly due to the much larger threshold gain, compared to that of the fundamental mode as long as the Zn diffusion depth outside the 5×5 μm² absorber aperture is over ~0.2 μm, which agrees well with the experimental results     

1.3-μm Pr-doped In-Ga-based fluoride fiber amplifiers pumped bygrating-fiber-pigtailed 0.98-μm-band laser diodes with a detunedwavelength of 1 μm

At most efficient pump wavelength, a praseodymium-doped In-Ga-based fluoride fiber is directly pumped by four 0.98-μm-band laser diodes. These lasing wavelengths are detuned from 0.98 to 1 μm by external selective optical feedback from fiber grating reflectors. Maximum signal output power of +13.5 dBm is obtained at 1.296 μm. Four-wavelength multiplexed signals at 1.296-1.311 μm are amplified with a deviation of gain less than 1.9 dB. By using the amplifier as a power booster, data of 2.5 Gb/s is successfully transmitted more than 100 km     

A parallel structure for CMOS four-quadrant analog multipliers andits application to a 2-GHz RF downconversion mixer

A parallel structure for a CMOS four-quadrant analog multiplier is proposed and analyzed. By applying differential input signals to a set of combiners, the multiplication function can be implemented. Based on the proposed structure, a low-voltage high-performance CMOS four-quadrant analog multiplier is designed and fabricated by 0.8 μm N-well double-poly-double-metal CMOS technology. Experimental results have shown that, under a single 1.2 V supply voltage, the circuit has 0.89% linearity error and 1.1% total harmonic distortion under the maximum-scale input 500 mV_p-p at both multiplier inputs. The -3 dB bandwidth is 2.2 MHz and the DC current is 2.3 mA. By using the proposed multiplier as a mixer-core and connecting a newly designed output buffer, a CMOS RF downconversion mixer is designed and implemented by 0.5 μm single-poly-double-metal N-well CMOS technology. The experimental results have shown that, under 3 V supply voltage and 2 dBm LO power, the mixer has -1 dB conversion gain, 2.2 GHz input bandwidth, 180 MHz output bandwidth, and 22 dB noise figure. Under the LO frequency 1.9 GHz and the total DC current 21 mA, the third-order input intercept point is +7.5 dBm and the input 1 dB compression point is -9 dBm     

Monolithic integration of an ARROW-type demultiplexer andphotodetector in the shorter wavelength region

A monolithic integration of an antiresonant reflecting optical waveguide (ARROW)-type demultiplexer and photodetector is discussed. The isolation was theoretically calculated to be -21.6 dB between the wavelengths of 0.78 and 0.88 μm, with a maximum detecting efficiency of 58% in a short demultiplexing/photodetecting length of 100 μm. The fundamental characteristic was demonstrated experimentally. This type of device can be applied to a wavelength division multiplexing (WDM) system with comparatively wide wavelength separation, e.g. 1.3- and 1.55-μm wavelengths     

Fabrication of variable bandwidth filters using arrayed-waveguidegratings

Variable bandwidth filters have been fabricated using silica-based N×N arrayed-waveguide gratings. The centre wavelengths are λ₀=1.55 μm for all channels. The 3 dB bandwidths are 40, 78, 116 and 154 GHz, for the filter with a path length difference ΔL=63 μm. In the filter with ΔL=8.6 μm, the 3 dB bandwidths are 414, 769, 1198 and 1608 GHz. The on-chip losses are 2.1-2.9 dB and sidemode suppression ratios are larger than 27 dB     

New short-wavelength laser emissions from optically pumped 13CD3OD

We report the discovery of 15 new laser emissions from ¹³ CD₃OD when optically pumped with a CW CO₂ laser. The wavelengths of these lines, ranging from 57.5 to 135.2 μm, are reported along with their polarization relative to the CO₂ pump laser, operating pressure and relative intensity. A three-laser heterodyne system was then used to measure the frequencies of 12 optically pumped laser emissions from this methanol isotope. These emissions range from 65.7 to 151.8 μm and are reported with fractional uncertainties up to 2·10^-7     

Polarization-insensitive SOA with a strained bulk active layer fornetwork device application

Current and wavelength characteristics for 1.55-μm semiconductor optical amplifiers (SOAs) containing bulk active layers with various tensile strains were investigated. The strain dependence of the gain-difference between the TE-mode and TM-mode (ΔG_TE-TM ) was almost linear having a waveguide-width over 0.8-1.5 μm. A -0.12% tensile-strained bulk SOA had very low ΔG_TE-TM of less than 0.8 dB for driving current ranging from 0 to 120 mA. The low-polarization-sensitive condition of SOAs with strained-bulk active layers was shown to yield very wide range in driving current and wavelength for network device applications     

A monolithic dual-band HgCdTe infrared detector structure

A monolithic HgCdTe photoconductive device structure is presented that is suitable for dual-band optically registered infrared photodetection in the two atmospheric transmission windows of 3-5 μm and 8-12 μm, which correspond to the mid-wave and long-wave infrared bands; MWIR and LWIR, respectively. The proposed structure employs a wider bandgap isolating layer between the two photosensitive layers such that an effective electrical barrier is formed thus prohibiting carrier transport between the two infrared absorbing layers of different cutoff wavelengths. The technology is demonstrated using a mature HgCdTe photoconductive device fabrication process. The resulting detectors have an MWIR cutoff of 5.0 μm, and LWIR cutoff of 10.5 μm     

A novel three-wavelength demultiplexer utilizing the two- andthree-guide couplers

A novel coupler-type demultiplexer fabricated by K⁺-ion exchange in soda-lime glass and applicable to three wavelengths with arbitrary wavelength spans is described. The output light-power extinction ratios of about -20 dB were measured for the operation wavelengths of 1.152, 1.310, and 1.523 μm. A simple method of designing for the structure parameters is also presented     

Low-power current-mode 0.9-V voltage regulator

A design for a low-power integrated 0.9-V voltage regulator for load currents up to 140 μA is presented. The circuit contains no external components and it stabilizes the voltage of a single battery cell of 1.1-1.6 V with a PSRR >40 dB over a frequency range of up to 30 kHz. The regulating circuit operates a current level and accomplishes automatic load-current limiting. Its r.m.s output noise is <4 μV over a frequency range of 10 Hz-8 kHz. The quiescent supply current is ≈40 μA     

A flat-field broadband spectrograph design

A planar spectrograph design is described that features a flat-field output and operates over a remarkably broad range of wavelengths. The grating facet positions are described by an iterative algorithm that ensures that light will arrive in phase at the focal point. There are no aberrations of any order at the design wavelength and aberrations near the design wavelength are simultaneously minimized. The peak intensity of the output varies less than 3 dB over a wavelength range of 1.46 to 1.64 μm. The spectrograph may be used as a demultiplexer in photonics systems using wavelength division multiplexing. The design easily accommodates hybrid integration of a linear detector array at the output