Keishi Takaki

Recorded Low Power Dissipation in Highly Reliable 1060-nm VCSELs for “Green” Optical Interconnection

1060-nm VCSELs with low power dissipation and high reliability are demonstrated. We designed 1060-nm VCSELs with double intracavity structure to achieve high reliability and low power dissipation for the optical interconnection. We performed evaluations of an error-free 10-Gbps operation at low bias current, and the recorded low power dissipation per data rate of 0.14 mW/Gbps was achieved. Even though the modulation amplitude of the input signal was as small as 75 mVp-p, the extinction ratio of 6.5 dB was observed. From accelerating aging tests with 4898 devices, no random failure was observed, and high reliability of 30 failures in term (FITs)/channel with a confidence level of 90% was achieved.

Recent advances in DFB lasers for ultradense WDM applications

State-of-the-art distributed feedback (DFB) laser modules integrated with a wavelength monitor are presented that provide excellent wavelength stability. By adopting unique and compact configuration, wavelength deviations of as small as a few picometers have been achieved. The laser modules are improved also in the scope of high power, high reliability, and wavelength tunability. Reliability test results of the DFB laser diodes and modules confirm a sufficiently long lifetime of more than 25 years and a small wavelength drift of less than /spl plusmn/3 pm. The developed laser modules are fully applicable to ultradense wavelength-division multiplexing applications with the current narrowest channel spacing of 25 GHz.

Reduced linewidth re-broadening by suppressing longitudinal spatial hole burning in high-power 1.55-/spl mu/m continuous-wave distributed-feedback (CW-DFB) laser diodes

For the first time, the impact of longitudinal photon density distribution and longitudinal carrier density distribution on the spectral linewidth re-broadening effect in single-electrode 1.55-/spl mu/m distributed feedback (DFB) laser diodes (LDs) is investigated experimentally in details. By optimizing the front-to-rear facet power ratio, the nonuniformity of the photon density distribution along the laser cavity is reduced, hence reducing the degree of longitudinal spatial hole burning (SHB). Using this optimized value of front-to-rear facet power ratio, the degree of longitudinal SHB can be further reduced through reduction of the nonuniformity of the longitudinal carrier density distribution by increasing the cavity length. As a result, the local stimulated emission is reduced, hence reducing linewidth re-broadening caused by longitudinal SHB. The outcomes of this analysis is being used fruitfully to design high-power 1.55-/spl mu/m DFB LDs exhibiting very narrow spectral linewidth of approximately 1.3 MHz at an output power of 175 mW under continuous-wave operation.

Recorded low power dissipation of 0.14 mW/Gbps in 1060 nm VCSELs for “Green” optical interconnection

Extremely low power dissipation of 0.14 mW/Gbps at 10 Gbps operation with as small as 75 mVp-p of modulation amplitude has been achieved in carefully designed InGaAs/GaAs-MQW 1060 nm VCSELs employed double intra-cavity structure.

Experimental demonstration of low jitter performance and high reliable 1060nm VCSEL arrays for 10Gbpsx12ch optical interconnection

No systematic studies on 1060nm high speed VCSELs have been reported in terms with reliability so far to our best knowledge. In this work, a systematic and intensive study on reliability has been performed for our 1060nm VCSELs consist of double intra-cavity and oxide confined structure with >70ps eye opening margin in Ib=3mA. Estimated power dissipation per bit rate of >5Gbps/mW at Ib=2mA was obtained from low series resistance and low drive voltage characteristics due to effective current injection in our double intra-cavity structure. Aging tests for 3,467pcs discrete non-hermetic VCSELs were performed under 6mA, 70°C to 120°C and up to 5,736 hours, which is equivalent to over 10million device hours in normal operating condition of 40°C and Ib=5mA. We found one degraded device due to the disconnection of the metal interconnecting layer, resulting in 81Fits (C.L.=90%) under Ea=0.35eV and no current accelerated factor. Also, their degradation of threshold current after 1,000 hours operation was less than 0.1mA under high stress condition of >40kA/cm2 and 120°C, which corresponds to more than hundreds year operation. No eye diagram degradation was observed as far as no large threshold current increase under the high stress condition up to 40kA/cm2. It is experimentally proven that inherent potentiality of the VCSELs with 1060nm InGaAs-QW and double intra-cavity structure would be applicable to the future large green data traffic system.

Low power optical interconnect at 10 Gbps with high efficiency 1060nm VCSEL

We developed a high speed, low power optical interconnect system using a high efficiency 1060 nm VCSEL. Clear eye diagrams are recorded at 10 Gbps with lower than 2 mA bias and 150 mVp-p modulation voltage.

Optical absorption coefficient of carbon-doped GaAs epitaxial layer by means of propagation -loss measurement of waveguide for long wavelength VCSEL

The optical absorption coefficient (α) for carbon-doped GaAs epitaxial layer by CBr<inf>4</inf> with doping range from 10¹⁸ to 10²⁰ cm⁻³ was measured for the first time. Obtained α<inf>GaAs:C</inf> was 2-times larger than α<inf>GaAs:Zn</inf> at 1300nm.

Spectral linewidth re-broadening and photon density distribution in 1550nm high power CW-DFB lasers

First investigation on spectral linewidth re-broadening due to photon density distribution has yielded optimized high-power (225mW) CW-DFB MQW lasers with very narrow linewidth (0.7MHz at 100mW).

20 Gbps optical link with high-efficiency 1060 nm VCSEL

Measurement results of a high speed, low power single channel optical link operating at 1060 nm are presented. The link is composed of low power VCSEL devices fabricated and provided by Furukawa Electric Co. Ltd. and a low cost OM2 fiber. Clear eye openings are observed at 20 Gbps with a 2 mA DC bias. A modulation voltage of 150 mVp-p results in a -4.1 dBm OMA at the fiber output in a back-to-back configuration, with 0.19 unit amplitude eye opening and 32 ps total jitter extrapolated to a 10-12 bit error ratio. The insertion of a 100 m-long OM2 fiber causes a small signal degradation due to low attenuation and dispersion. For an ideal index profile optimized for dual wavelength operation (850 and 1300 nm), the minimum modal dispersion of the fiber is in the vicinity of the current operation wavelength.

Enabling VCSEL technology for “Green” optical interconnect in HPC and Data Centers

State of the art VCSEL technology will be reviewed in terms of power consumption and reliability in order to realize the energy efficient HPC and Data Centers. Longer wavelength VCSEL seems promising candidate for the upcoming higher performance computes with energy saving.