Atsushi Takai

InGaAs/InGaAsP MQW electroabsorption modulator integrated with a DFB laser fabricated by band-gap energy control selective area MOCVD

The fabrication and basic characteristics of a InGaAs/InGaAsP multi-quantum-well (MQW) electroabsorption modulator with a novel structure integrated with a distributed-feedback (DFB) laser are presented. A fundamental study was performed on the applicability of the InGaAs/InGaAsP MQW structure to an electroabsorption-type modulator. Efficient attenuation small hole pileup and small chirp characteristics of a discrete modulator based on this MQW structure were demonstrated experimentally. A study of the controllability of in-plane band-gap energy by the use of selective-area metal-organic chemical vapor deposition (MOCVD) was also demonstrated. The modulator was monolithically integrated with a MQW DFB laser of the same material. Using a low-capacitance semi-insulating buried heterostructure, over 14 GHz modulation under high-light-output operations up to +10 dBm was achieved. Modulation at 10 Gb/s with a modulation voltage swing of only 1 V/sub pp/ demonstrates the potential value of this system for 1.55- mu m lightwave communications. >

200-Mb/s/ch 100-m optical subsystem interconnections using 8-channel 1.3-/spl mu/m laser diode arrays and single-mode fiber arrays

Synchronous parallel optical-fiber transmission is an attractive method for providing increased interconnection throughput and higher density in advanced information systems. Skew suppression (reducing transmission delay time variation), error-free fully DC-coupled data transmission capability, compactness, and low power consumption of modules are important requirements. In order to meet these requirements, we developed optical subsystem interconnections using long-wavelength laser diode arrays and single-mode fiber arrays. The major design criteria are discussed, especially as they are related to skew due to laser diode turn-on delay and receiver input optical power variation. The use of low-threshold-current laser diode arrays is an important design requirement. Based on the design criteria discussed in this work, we demonstrated and channel 200-Mb/s/ch 100-m transmission using compact (0.18 cc/ch/module), low power (total 280 mW/ch), fully integrated transmitter and receiver modules with an ECL (emitter coupled logic) interface. These modules include our new laser diode arrays with low threshold current of 3.2 mA. Performance results showed that these modules are very effective as interconnections between synchronously operating subsystems. >

Strained InGaAs/InAlAs MQW electroabsorption modulators with large bandwidth and low driving voltage

We demonstrate the improved modulation properties of a new strained InGaAs/InAlAs MQW electro-absorption modulator. This tensile strained MQW modulator shows low driving voltage (V/sub 15 dB/=1.2 V), large modulation bandwidth (f/sub 3 dB/>20 GHz), and a 10 Gbit/s eye pattern with a clear eye opening and high extinction ratio. The effective /spl alpha/ parameter determined from waveform deterioration is 0.6, which is low enough for multigigabit long-haul fiber transmission systems.<<ETX>>

High-extinction-ratio MQW electroabsorption-modulator integrated DFB laser fabricated by in-plane bandgap energy control technique

The local bandgap energy of an InGaAs/InGaAsP multiple quantum well (MQW) structure was precisely adjusted by in-plane Eg control in one-step selective area metalorganic chemical vapor deposition (MOCVD) growth. The technique was then applied to an MQW electroabsorption-modulator integrated distributed feedback (DFB) laser. Experimental results showed superior device characteristics, such as a high extinction ratio of 25 dB and low threshold current of 15 mA.<<ETX>>

Dependence of high-speed properties on the number of quantum wells in 1.55 mu m InGaAs-InGaAsP MQW lambda /4-shifted DFB lasers

The dependence of intrinsic dynamic properties, such as relaxation oscillation frequency, damping K-factor, and spectral chirping under 10-Gb/s direct modulation, on the number of quantum wells is systematically investigated in 1.55- mu m multiquantum-well lambda /4-shifted distributed-feedback lasers. The theoretical and experimental results indicate that the dependence of the above three factors on the number of quantum wells is clearly explained by the linear gain saturation of the quantum-well lasers. >

Factors limiting the spectral linewidth of CPM-MQW-DFB lasers

A spectral linewidth of 56 kHz is achieved by a CPM-MQW-DFB (corrugation-pitch-modulated multiquantum-well distributed feedback) laser at an output power of 25 mW. To separate effects of the white noise and 1/f noise in limiting the linewidth, the authors measured the delayed-heterodyne lineshape by using a short delay-fiber. The minimum spectral linewidth is shown to be limited by white noise.<<ETX>>

A new assembly architecture for multichannel single mode-fiber-pigtail LD/PD modules

A novel assembly architecture is developed for alignment and soldering between single-mode (SM) fiber arrays and laser-diode/photodiode (LD/PD) arrays. The image position detection method, by eliminating degrees of freedom for alignment, improves assembly throughput to twice that of conventional assembly architecture. The thermal shrinkage compensation method achieves high-precision soldering by canceling misalignments due to thermal shrinkage of assembly equipment and solder volume. As a result, assembly, through all processes, achieves +or-1.5- mu m precision, which corresponds to a +or-1-dB fluctuation of coupling efficiency. Based on this architecture, eight-channel SM-fiber-pigtail LD/PD modules were successfully assembled.<<ETX>>

Subsystem optical interconnections using long-wavelength LD and singlemode-fiber arrays

Subsystem optical interconnections for lengths of over 100 m are proposed. Single-mode fiber (SMF) arrays and very-low-threshold-current long-wavelength laser diode (LD) arrays realize small-skew and error-free interconnections. The LD turn-on delay and receiver risetime and falltime (t/sub r//t/sub f/) skews are considered in addition to the electronic and fiber skews, and a total skew of less than 1.65 ns is obtained. It is shown that an SMF array with a skew of 2.1 ps/m is needed to obtain a small skew. The LD array can be coupled with an SMF array to give high signal-to-noise ratio and error-free transmission. Driving each LD at a modulation current of six times the threshold current results in an LD turn-on delay skew of less than 500 ps. Wideband preamplifiers with low feedback resistivity reduce receiver t/sub r//t/sub f/ skew. The total skew of 1.65 ns gives a transmission speed of less than 150 MB/s (150 Mb/s/ch*8 ch) through a 100-m fiber array.<<ETX>>

Advantage of 1.55 mu m InGaAs/InGaAsP MQW-DFB lasers for reducing waveform degradation and dispersion penalty for 2.5 Gb/s long-span normal fiber transmission

The advantage of 1.55- mu m multiquantum-well (MQW) distributed-feedback (DFB) lasers over conventional bulk lasers for normal fiber transmission is shown by evaluating the waveform degradation and the dispersion penalty theoretically and experimentally. The dispersion penalty expected for 70-km transmission is shown to be smaller than 1 dB at 2.5 Gb/s when the bias current is 1.1 times the threshold bias.<<ETX>>

800 Mbit/s/ch/spl times/12 ch, true DC-coupled parallel optical interconnects using single-mode fiber and 1310 nm LD array

We developed 800 Mbit/s/ch, 12 ch, DC-coupled parallel optical interconnect modules, and confirmed high speed parallel transmission. For skew reduction between channels, we use single mode fiber array. In transmitter module, laser turn-on delay time is reduced by edge-pulse modulation method. In receiver module, 4 GHz-bandwidth receiver IC enables one to suppress waveform distortion caused by optical power variation. For assemblability and reliability, planar micro lens arrays are used for optical coupling and hermetic sealing.