Design and optimization of evanescently coupled waveguide photodiodes

We present the design and optimization of evanescently coupled waveguide photodiodes (EC-WPDs) based on the coupling modes theory and the beam propagation method. Efficient focalization of the optical power in the absorber is achieved by an appropriate choice of index matching layers of EC-WPDs. Numerical simulation shows that high-speed (40 GHz), high quantum efficiency (81%) and high linearity photodiodes can be achieved, and EC-WPDs are promising devices for future optical communication systems.     

Monolithic GaInAs quad-p-i-n photodiodes for polarization-diversity optical receivers

GaInAs quad p-i-n photodiodes which monolithically integrate two sets of twin-p-i-n photodiodes have been fabricated for a polarization-diversity optical receiver designed for practical coherent lightwave transmission systems. Each p-i-n photodiode achieved a very small capacitance of 616-66 fF, a dark current of 6 pA-6 nA, and a high quantum efficiency of 86-88%. The cutoff frequency of the twin-p-i-n photodiodes exceeded 13 GHz. A common-mode rejection ratio (CMRR) of -30 dB was measured for the two sets up to 10 GHz. The optical/electrical crosstalk between the two sets of twin-p-i-n photodiodes was about -40 dB at 14 GHz.<>     

The impact of a large bandgap drift region in long-wavelengthmetamorphic photodiodes

A comparative study of two types of metamorphic double heterojunction long-wavelength photodiodes on GaAs substrates is performed in terms of their bandwidths and responsivities. A p-i-i-n heterostructure with a large bandgap drift layer (I-InAlAs) at the cathode end of the photoabsorption region (i-InGaAs) is compared experimentally and theoretically to a p-i-n structure without a drift layer. Both types of photodiodes were fabricated using an InGaAs-InGaAlAs-InAlAs double heterostructure design to simultaneously achieve high bandwidths and high responsivities. The inclusion of an I-InAlAs drift region resulted in p-i-i-n photodiodes with larger bandwidths than p-i-n photodiodes with the same areas, or conversely a p-i-i-n photodiode can be made larger than a comparable p-i-n photodiode, but achieve the same bandwidth. Therefore, p-i-i-n photodiodes provide larger optical fiber alignment tolerances and better coupling efficiency than p-i-n photodiodes with the same bandwidths, p-i-i-n photodiodes with 10-μm-diameter optical windows typically exhibited low dark currents of 500 pA at 5-V bias, responsivities of 0.6 A/W, and a -3-dB bandwidth of 38 GHz for 1.55-μm operation     

Evanescently coupled photodiodes integrating a double-stage taper for 40-Gb/s applications-compared performance with side-illuminated photodiodes

The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes.     

30 Gb/s Over 100-m MMFs Using 1.1-$mu$ m Range VCSELs and Photodiodes

We developed 1.1-mum-range vertical-cavity surface-emitting lasers based on InGaAs-GaAs quantum wells, back-illuminated InGaAs photodiodes, and transimpedance amplifiers (InP heterojunction bipolar transistor) for high-speed optical interconnection. Clear eye opening operation and error-free transmission at 30 Gb/s over 100-m multimode fibers (GI32) were successfully achieved for the first time.     

On-Chip Optical Interconnect

We describe a cost-effective and low-power-consumption approach for on-chip optical interconnection. This approach includes an investigation into architectures, devices, and materials. We have proposed and fabricated a bonded structure of an Si-based optical layer on a large-scale integration (LSI) chip. The fabricated optical layer contains Si nanophotodiodes for optical detectors, which are coupled with SiON waveguides using surface-plasmon antennas. Optical signals were introduced to the optical layer and distributed to the Si nanophotodiodes. The output signals from the photodiodes were sent electrically to the transimpedance-amplifier circuitries in the LSI. The signals from the photodiodes triggered of the circuitries at 5 GHz. Since electrooptical modulators consume the most power in on-chip optical interconnect systems and require a large footprint, they are critical to establish on-chip optical interconnection. Two approaches are investigated: 1) an architecture using a fewer number of modulators and 2) high electrooptical coefficient materials.     

An integrated optical receiver for multilevel data communication over large core step index plastic optical fiber

A BiCMOS integrated optical receiver with high sensitivity and good linearity is presented. An automatic gain control transimpedance amplifier (TIA) and linear post amplifiers are used to maintain a high linearity with multilevel modulation. Using multilevel signaling and large-diameter integrated photodiodes make the presented optical receiver suitable for small-bandwidth high-attenuation large-core PMMA step index plastic optical fiber. A measured sensitivity of −31 dBm (BER = 10⁻⁹) at 250 Mb/s is presented for a binary signal. A data rate of 500 Mb/s and a sensitivity of −25 dBm (BER = 10⁻⁹) are achieved with four-level pulse amplitude modulation (4-PAM). An error-free transmission over 40 m PMMA step index plastic optical fiber was achieved at 500 Mb/s using 4-PAM signaling with the presented multilevel optical receiver.     

Three-Optical-Port Module for Monolithic Optical Gate Integrated With Photodiode and Electroabsorption Modulator

Compact and stable three-optical-port modules are developed for optical gate devices monolithically integrated with photodiodes and electroabsorption modulators. The module has the same package size as ordinary laser-diode (LD) modules, and has three pigtailed fibers on two sides and the top. The module has high coupling efficiency and high stability for every optical port     

Metamorphic graded bandgap InGaAs-InGaAlAs-InAlAs doubleheterojunction p-i-I-n photodiodes

High-speed metamorphic double heterojunction photodiodes were fabricated on GaAs substrates for long-wavelength optical fiber communications. The high quality linearly graded quaternary InGaAlAs metamorphic buffer layer made possible the growth of excellent InGaAs-InGaAlAs-InAlAs heterostructures on GaAs substrates. The use of a novel double heterostructure employing an InGaAlAs optical impedance matching layer, a chirped InGaAs-InAlAs superlattice graded bandgap layer (SL-GBL), and a large bandgap i-InAlAs drift region enabled photodiodes to achieve a low dark current of 500 pA, a responsivity of 0.6 A/W, and a -3 dB bandwidth of 38 GHz at -5 V reverse bias for 1.55 μm light. The effect of accumulated charges at the InGaAs-InAlAs heterointerface was examined through a comparison of the dark currents of InGaAs-InAlAs and InGaAs-InP abrupt single heterojunction photodiodes; to photodiodes with chirped InGaAs-InAlAs SL-GBLs. The charge accumulation effects observed in abrupt heterojunction devices were suppressed by including a chirped InGaAs-InAlAs SL-GBL between the InGaAs absorption layer and InAlAs drift layer. The effect of passivation techniques was evaluated by comparing dark currents of unpassivated photodiodes and photodiodes passivated with either polyimide or SiN_x. The enhancement of photodiode bandwidth through the inclusion of a transparent large bandgap I-InAlAs drift region was verified by comparing the bandwidths of the P-i-I-N photodiodes that have I-InAlAs between i-InGaAs photoabsorption layer and N⁺ InAlAs cathode to conventional P-i-N photodiodes without a drift region     

Analysis of partially depleted absorber waveguide photodiodes

This paper presents the analysis and characterization of partially depleted absorber (PDA) photodiodes. Coupling to these photodiodes is achieved through a planar short multimode waveguide (PSMW) structure. Electric transport in the PDA structure has been investigated and an equivalent electric circuit was developed. Measurements on 5/spl times/20 /spl mu/m/sup 2/ PSMW PDA photodiodes have shown 0.80 A/W responsivity with a fiber mode diameter as high as 6 /spl mu/m. The transverse electric/transverse magnetic polarization dependence was <0.5/spl plusmn/0.3 dB with -1-dB input coupling tolerances as high as /spl plusmn/2.0 and /spl plusmn/1.3 /spl mu/m for horizontal and vertical directions. The -3-dB bandwidth was 50 GHz, and the -1-dB compression current at 40 GHz was 17 mA corresponding to +4.5 dBm radio frequency (RF) power. Compared to similar evanescently coupled p-i-n photodiodes, the saturation current has been significantly improved while maintaining comparable bandwidth and high responsivity.     

Silicon Geiger mode avalanche photodiodes

In this letter we present the results regarding the electrical and optical characterization of Geiger mode silicon avalanche photodiodes(GMAP) fabricated by silicon standard planar technology. Low dark count rates,negligible afterpulsing effects,good timing resolution and high quantum detection efficiency in all the visible range have been measured. The very good electro-optical performances of our photodiodes make them attractive for the fabrication of arrays with a large number of GMAP to be used both in the commercial and the scientific fields,as telecommunications and nuclear medical imaging.     

Measurement of nonlinear distortion in photodiodes

The 2nd-order nonlinear distortion of avalanche photodiodes (TIXL-55, C-20817) was found to be less than ?60 dB for an incident average optical power of ?20 dBm modulated at a peak depth of 75%. p-i-n photodiodes (HP 5082-4207) were found to have 2nd-order-distortion levels below the noise level. A method using three independent optical signal sources was employed in the measurement.     

Avalanche photodiodes on silicon photonics

Silicon photonics technology has drawn significant interest due to its potential for compact and high-performance photonic integrated circuits.The Ge-or Ⅲ-Ⅴ material-based avalanche photodiodes integrated on silicon photonics provide ideal high sensitivity optical receivers for telecommunication wavelengths.Herein,the last advances of monolithic and hetero-geneous avalanche photodiodes on silicon are reviewed,including different device structures and semiconductor systems.     

高速光检测器和高速光接收机进展

本文综述了近年来微波光电子学中高速光检测器和高速光接收机的进展，分析并对比了各种光电二极管的响应速度、噪声及暗电流特性；指出光波导与ＭＳＭ、ＰＩＮ为代表的高速光电二极管以及ＨＥＭＴ、ＨＢＴ等低噪声微波器件的光电集成，是高速光接收机的发展趋势，行波光检测器作为高速分布参数光电器件，光波导与光电二极管的融合，光场效应晶体管以及掺铒光纤放大器的应用，都是值得重视的发展动态。     

High speed InGaAs/InP p-i-n photodiodes fabricated on asemi-insulating substrate

High speed, mass-produced InGaAs-InP p-i-n photodiodes have been fabricated on a semi-insulating substrate. The FWHM (full width at half maximum) impulse response of a 25-μm² device has been measured to be under 16 ps, entirely limited by the measurement system. The high speed of this structure was achieved by scaling the area down to 25 μm² and the intrinsic layer thickness down to 0.3 μm. Further scaling of this structure is possible, and bandwidths in excess of 200 GHz should be achievable. This structure is also useful for integration with bias tees, matching networks, and optical and electronic preamplifiers     

Design and analysis of micromechanical tunable interferometers forWDM free-space optical interconnection

This paper proposes a new concept of high density chip-to-chip optical interconnection based on wavelength division multiplexing (WDM), which can be realized as a microelectromechanical system (MEMS) device. The output signals from a preprocessing integrated circuit (IC) chip (N channels) are converted to optical signals of different wavelengths by using wavelength tunable laser diodes and projected onto an array of wavelength-selective photodiodes. Channel connection is made by wavelength matching between the light sources and detectors, by using micromechanical Fabry-Perot interferometers. In this scheme arbitrary 1 to 1 connection as well as 1 to N or N to 1 connection is available. Since the input/output connections are made in an optical manner, the switching state can be reconfigured and the whole switching system can be integrated in a compact space. We have investigated design principle of the micromechanical Fabry-Perot interferometers for tunable photodiodes to maximize the switching contrast and channel density in a given wavelength range. The preliminary interferometer arrays are implemented by silicon-based surface micromachining     

The Monolithic Integration of a Wavelength-Demultiplexer With Evanescently Coupled Uni-Traveling-Carrier Photodiodes

In this letter, we discuss a novel integration of a wavelength demultiplexer with a pair of uni-traveling-carrier photodiodes (UTC-PDs). With this integrated module, we could separate incoming wavelengths of 1530 and 1550 nm, which are near the wavelengths utilized for digital and analog signal transmission in coarse wavelength-division multiplexing (CWDM) systems. The integrated UTC-PDs exhibited the following advantages: a wide 3-dB bandwidth (25 GHz), a reasonable responsivity (0.35 A/W), and a high-saturation-current (>17 mA). A low level of radio frequency crosstalk between the two photodiodes (less than -15 dB) could also be achieved for a wide frequency range (near DC to 40 GHz). This is low enough for the multichannel receivers in a WDM broadcast system. In addition, by use of our module, we demonstrated digital/analog signals co-transmission and demultiplexing with speeds of 2.5 Gb/s at optical wavelengths of 1530 and 1550 nm.     

Temperature-immune and intensity-referenced pressure sensor based on strain-induced quadratic-chirped fibre bragg grating

A technique for temperature-immune pressure measurement using a strain-induced quadratic-chirped fibre Bragg grating by differential optical power detection is demonstrated. Linear pressure measurement up to 20 kPa with a resolution of 0.05 kPa and thermal stability less than 2% full-scale for a temperature range from 0 to 80degC are achieved using pin photodiodes detection, without any temperature compensation     

Application specific spectral response with CMOS compatiblephotodiodes

Several methods are presented for realizing photodiodes with independent spectral responses in a standard CMOS integrated circuit process. Only the masks, materials, and fabrication steps inherent to this standard process were used. The spectral responses of the photodiodes were controlled by (1) using the SiO₂ and polycrystalline Si as thin-film optical filters, (2) using photodiodes with different junction depths, and (3) controlling the density of the interfacial trapping centers by choosing which oxide forms the Si/SiO ₂ interface. Also presented is an example method for constructing photo-spectrometers using these spectrally-independent photodiodes. This method forms weighted sums of the photodiodes' outputs to extract spectrographic information