Mikihiro Kajita

Complete polarization control of 8×8 vertical‐cavity surface‐emitting laser matrix arrays

Polarization of 8×8 vertical cavity surface emitting laser (VCSEL) arrays is completely controlled. These index‐guided VCSELs have a 6×5 μm rectangular poststructure consisting of DBR mirrors. All 64 VCSELs emit fundamental single‐mode and linearly polarized light with a polarization angle deviation of only 2.9°. Their light output characteristics are almost the same as those of conventional 6×6 μm polarization‐uncontrolled VCSELs.

A 1ps-Resolution Jitter-Measurement Macro Using Interpolated Jitter Oversampling

An in-field real-time successive jitter-measurement macro is developed. It features interpolated jitter oversampling and feedforward calibration that help attain 1ps resolution and a hierarchical Vernier jitter-measurement technique that exploits the trade-off between rms and deterministic jitter measurement characteristics

A two-dimensional optical parallel transmission using a vertical-cavity surface-emitting laser array module and an image fiber

The possibility of high-density optical parallel transmission using an arrayed vertical-cavity surface-emitting laser (VCSEL) and an image fiber was demonstrated. Thirty six (6/spl times/6) laser lights from a VCSEL-array module were transmitted through an image fiber with a 460-/spl mu/m diameter and consisting of 10,000 super-thin micro cores. The optical crosstalk was measured spatially and dynamically, and was less than -27 dB from dc to 3 GHz when a 1-m-long image fiber was used. We have actually transmitted bit data at a rate of 1 Gb/s, and the bit-error rate became 1/spl times/10/sup -8/ at the average received power of -27.7 dBm.

A 1-ps Resolution Jitter-Measurement Macro Using Interpolated Jitter Oversampling

This paper reports the development of an in-field real-time successive jitter-measurement macro whose features include 1-ps resolution jitter measurement. The newly developed jitter-measurement macro has four key features: 1) interpolated jitter oversampling; 2) a hierarchical Vernier delay line; and 3)feedforward calibration, each of which helps attain high jitter-measurement resolution; as well as 4) an oversampling rate and measurement range-control technique. A test chip of the macro has been fabricated in a 90-nm process. It successfully measures small random jitter with 1-ps resolution, and large deterministic jitter can also be measured by extending the jitter-measurement range by a factor of 4

Temperature characteristics of a vertical-cavity surface-emitting laser with a broad-gain bandwidth

Temperature-insensitive characteristics are of great importance in implementing the actual applications of vertical-cavity surface-emitting lasers (VCSELs) because of the temperature change in the surroundings. To extend the operational temperature range of such lasers, we fabricated a VCSEL with a broad gain bandwidth. The active layers in VCSELs consist of multiple quantum wells (MQWs) with different bandgap energies. From the change in the threshold current, with temperature as a parameter, we found that the operational temperature range of a VCSEL with a broad gain bandwidth is more than 20/spl deg/C wider than that of conventional VCSELs, whose active layers consist of a single type of MQW. We demonstrate that the extended-gain bandwidth gives better temperature characteristics. In addition, we simulated the structure of the active layers, and the optimized structure resulted in a 1-mW light output power at less than 5 mA in a single transverse mode oscillation from 20-70/spl deg/C. >

Control of light-output polarization for surface-emitting-laser type device by strained active layer grown on misoriented substrate

We propose and demonstrate control of light-output polarization for surface-emitting laser-type devices by using strained quantum-well active layers grown on a misoriented substrate. This structure has slightly asymmetric strain tensor elements on the surface plane. Due to orbital-strain interaction, the valence band structures change and the optical transition matrix element depends on the polarization of the light. Here, theoretical analysis and experimental results on the direction of misorientation are described, and it is shown that how the polarization of the light-output is related to asymmetry in strain tensors. For the devices, which have In/sub 0.2/Ga/sub 0.8/As active layers grown on a 2-degree-off-(100) GaAs substrate toward (111)B, the light-output is polarized in [01~1] with the reproducibility of as high as 88%. This highly controlled polarization is probably due to the combination of converse piezoelectric effect and asymmetry in the lattice mismatch on the surface caused by misorientation. >

A 1.1V 35μm × 35μm thermal sensor with supply voltage sensitivity of 2°C/10%-supply for thermal management on the SX-9 supercomputer

Presented here is a thermal sensor, based on transistor off-leakage current, that allows measurement error of less than 3.1degC at 90degC and less than 2degC at 10% Vdd deviation. For experimental evaluation, 11 thermal sensors, each of which occupied only 35 mum times 35 mum area, were placed on a chip, and both the location of a hotspot and the overall temperature distribution were successfully measured and agreed with simulation.

Thermal Analysis of Laser-Emission Surface-Normal Optical Devices with a Vertical Cavity

Laser-emission surface-normal optical devices with a vertical cavity are expected to be key devices for optical interconnections. Thermal characteristics improvement is necessary for a large-scale-integrated two-dimensional array which increases the number of optical interconnections. To optimize the device structures to obtain good thermal characteristics, the temperature rise of distributed Bragg reflectors and an active layer must be known. Here, we report on the first evaluation of temperature rise in both regions, and it is found that the temperature rise is small for a compact double-mesa structure which allows a single lateral-mode oscillation. In addition, we measured the thermal crosstalk between the above compact devices, and it is found that the thermal crosstalk between one-dimensional array devices is small enough when each device operates at a few milliamperes.

A 1-to-2GHz 4-Phase On-Chip Clock Generator with Timing-Margin Test Capability

A clock generator fabricated in 90nm CMOS occupies 300times128mum2 die area and dissipates 40mW at 1.2V. An interleaved clock-edge control technique extends the frequency tuning range and enables control of both rising and falling edge timing. A clock-period dithering technique enhances frequency tuning resolution. Disturbance-control functions that control jitter, duty cycle, and clock skew make timing margin testing possible

1-Gb/s modulation characteristics of a vertical-cavity surface-emitting laser array module

Vertical-cavity surface-emitting lasers (VCSELs) are promising devices for low-cost optical data communications. We fabricated an 8-channel VCSEL array module that is easily push/pull-connected to a mechanically transferable (MT) fiber connector. Modal noise had little adverse effect on bit-error-rate (BER) performance. A BER measurement of 8-channel VCSELs recorded a sensitivity of less than -23.7 dBm at 1 Gb/s and BER=10/sup -11/.