Influence of free carrier plasma effect on carrier-inducedrefractive index change for quantum-well lasers

The influence of the free carrier component due to the plasma effect on carrier-induced refractive index change and its dependency on polarization for multiple-quantum-well (MQW) and bulk lasers are experimentally studied. The ratios of the component to the total index change, R_fc, are 0.6, 0.4, and 0.1 for 1.3-μm MQW, 1.3-μm bulk, and 0.8-μm MQW lasers, respectively. The TM/TE polarization ratios of the component, R_TMTE/, are 0.8 and 0.3 for 1.3-μm MQW and 0.8-μm MQW lasers. The relationship between the index change and the carrier overflow (to barrier and separate confinement heterostructure layers) for MQW lasers is also discussed. Large R_fc and R_TMTE/ for the 1.3-μm MQW laser result from the carrier overflow     

Low threshold room temperature pulsed and -57°C CW operationsof 1.3 μm GaInAsP/InP circular planar buried heterostructuresurface-emitting lasers

Room temperature pulsed lasing operation of a 1.3-μm GaInAsP/InP vertical-cavity surface-emitting laser has been achieved by using an effective carrier confinement of circular planar buried heterostructure (CPBH) and high reflectivity SiO₂/Si dielectric multilayer mirrors. The threshold current for a device having a nearly 12-μm-diameter active region was 34 mA at 24°C under pulsed operation. The optimized window cap structure reduces the series resistance to 6~15 Ω. Continuous wave lasing was also obtained up to -57°C, and the threshold below -61°C was still lower than 22 mA     

1.3 μm multiquantum well decoupled confinement heterostructure(MQW-DCH) laser diodes

A 1.3-μm multi-quantum-well decoupled confinement heterostructure (MQW-DCH) laser diode has been developed. This structure introduces internal barriers between the active quantum wells and the optical waveguide. It is thus possible to have, at the same time, deep quantum wells to prevent carrier leakage and a strong optical waveguide with a high confinement factor. The barrier parameters have been optimized using numerical modeling tools, and the DCH laser diode has been built using chemical beam epitaxy. The broad-area transparency current density is 140 A-cm^-2, the internal efficiency is 0.83, the waveguide loss is 5 cm^-1. and T₀ = 62 K. Ridge waveguide laser diodes have a room temperature threshold of 8 mA and an efficiency of 0.32 mW/mA     

AlGaInP microcavity light-emitting diodes at 650 nm on Gesubstrates

We demonstrate microcavity light emitting diodes (MCLEDs) emitting at 650 nm on Ge substrates. Ge has the advantage of lower cost and higher strength compared to GaAs substrates. The multi-quantum well microcavity devices consisted of AlGaAs-based distributed Bragg reflector (DBR) mirrors, AlGaInP active material with an additional 5-μm p-Al_0.55Ga_0.45As current spreading layer on top of the p-DBR. A maximum external quantum efficiency of 4.35% and an optical power higher than 5 mW was obtained for a device with 200-μm diameter. The results indicate the potential use of MCLEDs on Ge for visible LEDs     

1.3-μm InAsP modulation-doped MQW lasers

The effect of both n-type and p-type modulation doping on multiple-quantum-well (MQW) laser performances was studied using gas-source molecular beam epitaxy (MBE) with the object of the further improvement of long-wavelength strained MQW lasers. The obtained threshold current density was as low as 250 A/cm² for 1200-μm-long devices in n-type modulation-doped MQW (MD-MQW) lasers. A very low CW threshold current of 0.9 mA was obtained in 1.3-μm InAsP n-type MD-MQW lasers at room temperature, which is the lowest ever reported for long-wavelength lasers using n-type modulation doping, and the lowest value for lasers grown by all kinds of MBE in the long-wavelength region. Both a reduction of the threshold current and the carrier lifetime in n-type MD MQW lasers caused the reduction of the turn-on delay time by about 30%. The 1.3-μm InAsP strained MQW lasers using n-type modulation doping with very low power consumption and small turn-on delay time are very attractive for laser array applications in high-density parallel optical interconnection systems. On the other hand, the differential gain was confirmed to increase by a factor of 1.34 for p-type MD MQW lasers (N_A=5×10¹⁸ cm ^-3) as compared with undoped MQW lasers, and the turn-on delay time was reduced by about 20% as compared with undoped MQW lasers. These results indicate that p-type modulation doping is suitable for high-speed lasers     

The sublinear relationship between index change and carrier densityin 1.5 and 1.3 μm semiconductor lasers

The carrier-induced index change was measured using a novel injection-reflection technique in combination with differential carrier lifetime data. The observed relation between index change and injected carrier density at bandgap wavelength is nonlinear and is approximately given by δn_act=-6.1×10^-14 ( N)^0.66 for a 1.5-μm laser and δn _act=-1.3×10^-14 (N)^0.68 for a 1.3-μm laser. The carrier-induced index change for a 1.3-μm laser at 1.53-μm wavelength is smaller and is given by δn _act=-9.2×10^-16 (N)^0.72      

Characteristics dependence on confinement structure and single-modeoperation in 2-μm compressively strained InGaAs-lnGaAsP quantum-welllasers

The optimum confinement layer structure in 2-μm compressively strained InGaAs-InGaAsP lasers is experimentally studied. Beside the carrier overflow and absorption loss in the confinement layers, the intervalence band absorption and/or Auger recombination play an important role in laser characteristics. More attention should be paid to the confinement structure to reduce the carrier density. We obtained a better laser performance with an energy difference between the bandgap of the optical confinement layer and the laser transition energy of 280-300 meV. A distributed-feedback (DFB) laser operating at 2.043 μm has been realized with the threshold current as low as 6 mA and the maximum output power of 6 mW. The differential quantum efficiency and the characteristic temperature are 16% and 59 K, respectively     

Low-threshold 1.5 μm compressive-strained multiple- andsingle-quantum-well lasers

Design considerations for low-threshold 1.5-μm lasers using compressive-strained quantum wells are discussed. Parameters include transparency current density, maximum modal gain, bandgap wavelength, and carrier confinement. The optical confinement for a thin quantum well in the separate-confinement heterostructure (SCH) and the step graded-index separate-confinement heterostructure (GRINSCH) are analyzed and compared. 1.5-μm compressive-strained multiple- and single-quantum-well lasers have been fabricated and characterized. As a result of the compressive strain, the threshold current density is loss limited instead of transparency limited. By the use of the step graded-index separate-confinement heterostructure to reduce the waveguide loss, a low threshold current density of 319 A/cm² was measured on compressive-strained single-quantum-well broad-area lasers with a 27 μ oxide stripe width     

Absorption loss coefficient of the active layer for 1.48-μm bulkand MQW lasers

It is shown that the absorption loss coefficient of the active layer for 1.48-μm bulk lasers is 66 cm^-1 which is between 45 and 107 cm^-1 for 1.3-μm bulk lasers and for 1.55-μm bulk lasers, respectively. It is also described that the absorption loss coefficient of the active layer for 1.48-μm multiple-quantum-well (MQW) lasers is 28 cm^-1 which is about two-fifths of that for 1.48-μm bulk lasers. Therefore, the high slope efficiency of the 1.48-μm MQW lasers is attributed not only to the small optical confinement factor but also to the small absorption loss coefficient of the active layer     

Design and fabrication of low-threshold 1.55-μm graded-indexseparate-confinement heterostructure strained InGaAsPsingle-quantum-well laser diodes

This paper presents a guideline for designing an optimum low-threshold 1.55-μm graded-index (GRIN) separate confinement-heterostructure (SCH) strained InGaAsP single quantum-well (SQW) laser diode (LD). The guideline was formulated based on the results of numerical and experimental analysis. After calculating the sheet carrier density at the lasing threshold, the guideline was obtained by considering the tradeoff between carrier and optical confinements in the well: the GRIN layer energy gap should be varied parabolically from InP to InGaAsP having a band gap wavelength of 1.1 μm to inject a large number of carriers into the well, and the thickness of one side of the GRIN layer should be more than 300 nm to keep a strong optical confinement. The GRIN SQW LD designed using the guideline has a J_th as low as 98 A/cm² at a cavity length of 5 mm, which proves the guideline is effective for designing low-threshold 1.55-μm GRIN SQW LDs     

Time compression multiplex transmission system using a 1.3 μmsemiconductor laser as a transmitter and a receiver

A bidirectional system using 1.3 μm lasers as a transmitter and a receiver are investigated. The lasers considered are commercially available Fabry-Perot and distributed-feedback lasers. It is found that the poor performance of a laser receiver, compared to a PIN receiver, stems from three factors: low responsivity, high capacitance, and polarization dependence of responsivity, high capacitance, and polarization dependence of responsivity. The effect of each factor is evaluated. It has been clarified that the polarization dependence of sensitivity originates from the TE and TM modes dependence of both mode confinement factor and reflection at a facet. Using the measured parameters, 1.3-μm laser receiver sensitivity for a 10^-9 error rate is estimated. Burst data transmission experiments show that estimated sensitivities agree well with the measured values. Optical ping-pong transmission distance of narrowband services is determined based on estimated sensitivity     

Strain-compensated 1.3-μm AlGaInAs quantum-well lasers withmultiquantum barriers at the cladding layers

Strain-compensated 1.3-μm AlGaInAs graded-index separate confinement heterostructure (GRINSCH) lasers with multiquantum barrier (MQB) at both the nand p-cladding layers are comprehensively studied and compared with the conventional GRINSCH lasers. It is found that the lasers with MQBs exhibit lower threshold current, higher maximum output power and better temperature characteristics because of the enhanced barrier height for carrier leakage. The characteristic temperature is improved as much as 10 K and the vertical far-field angle is also reduced from 38° to 32° as compared to the conventional counterpart     

Optimum index profile of the perfluorinated polymer-based GIpolymer optical fiber and its dispersion properties

The significant advantages in bandwidth and low material dispersion of perfluorinated (PF) polymer-based graded-index polymer optical fiber (GI POF) are theoretically and experimentally reported for the first time. It is confirmed that the low attenuation and low material dispersion of the PF polymer enables 1 Gb/s km and 10 Gb/s km transmission at 0.85-μm and 1.3-μm wavelengths, respectively. The PF polymer-based CI POF has very low material dispersion (0.0055 ns/nm·km at 0.85 μm), compared with those of the conventional PMMA-based POF and of multimode silica fiber (0.0084 ns/nm km at 0.85 μm). Since the PF polymer-based GI POF has low attenuation from the visible to near infrared region, not only the 0.65-μm wavelength which is in the low attenuation window of the PMMA-based GI POF, but other wavelengths such as 0.85-μm or 1.3-μm etc. can be adopted for the transmission wavelength. It is clarified in this paper that the wavelength dependence of the optimum index profile shape of the PF polymer-based GI POF is very small, compared to the optimum index profile shape of the silica-based multimode fiber. As a result, the PF polymer-based GI POF has greater tolerance in index profile variation for higher speed transmission than multimode silica fiber. The impulse response function of the PF polymer-based GI POF was accurately analyzed from the measured refractive index profile using a Wentzel, Kramers, Brillouin (WKB) numerical computation method. By considering all dispersion factors involving the profile dispersion, predicted bandwidth characteristic of the PF polymer-based GI POF agreed well with that experimentally measured     

Modelocking of interferometric Y-lasers in an external cavity

The first report on active modelocking of interferometric Y-lasers in an external cavity are reported. Pulse widths between 20 and 30 ps for 1.3-μm and 1.55-μm devices were achieved by modulation of the injection current synchronously to the external cavity roundtrip frequency. A time-bandwidth-product of 0.97 was determined for 1.55-μm devices     

Aging analysis of nMOS of a 1.3-μm partially depleted SIMOX SOItechnology comparison with a 1.3-μm bulk technology

Hot carrier degradation of nMOS of a 1.3-μm partially depleted rad-hard SOI CMOS technology is analyzed in detail. The relative importances of the maximum electric field, the localization of the trapped charges, and the LDD structure are pointed out through two-dimensional simulations and systematic comparisons with a 1.3-μm CMOS bulk technology. It is shown that the higher degradation rate of the SOI technology logically results from the contradictory constraints between rad-hardness (low-temperature process) and hot carrier resistance requirements. An annealing scheme comparable to the bulk one would lead to similar degradations     

Optical WDM transceiver module using wavelength-selective couplerand WDM-PD for optical access networks

A new optical wavelet division multiplexing (WDM)-transceiver module has been designed and fabricated for optical access networks. Conventional 1.3/1.55-μm WDM-coupler and Y-branch were replaced by a new wavelength-selective coupler in order to reduce module size. A new WDM-photodiode (PD), which was photosensitive to 1.3 μm light and transparent to 1.55 μm light, and a 1.55-μm PD were arranged in series along the optical axis. An MQW-FP-LD was used as a 1.3-μm transmitter. Fundamental characteristics were measured and discussed. Evaluation results, P_out of 0 dBm, responsivity of 0.36 A/W at 1.31 μm and 0.74 A/W at 1.55 μm, and IMD2 of -76.2 dBc, imply that this WDM-transceiver module design is promising to application for optical access networks     

Crosstalk characteristics of a 1.3-μm/1.5-μm wavelengthdemultiplexing photodetector using laser-assisted MOMBE growth

This paper demonstrates a monolithic 1.3-μm/1.5-μm wavelength demultiplexing photodetector fabricated using Ar ion laser-assisted metal organic molecular beam epitaxy (MOMBE) growth. Reduction of crosstalk to -24 dB is accomplished in both 1.3-μm and 1.5-μm wavelength regions. The dependence of the crosstalk on the coupling efficiency between the fiber and device and the polarization dependence of the responsivity is also discussed     

High-performance 0.10-μm CMOS devices operating at roomtemperature

The authors have fabricated 0.10-μm gate-length CMOS devices that operate with high speed at room temperature. Electron-beam lithography was used to define 0.10-μm polysilicon gate patterns. Surface-channel type p- and n-channel MOSFETs were fabricated using an LDD structure combined with a self-aligned TiSi₂ process. Channel doping was optimized so as to suppress punchthrough as well as to realize high transconductance and low drain junction capacitance. The fabricated 0.10-μm CMOS devices have exhibited high transconductance as well as a well-suppressed band-to-band tunneling current, although the short-channel effect occurred somewhat. The operation of a 0.10-μm gate-length CMOS ring oscillator has been demonstrated. The operation speed was 27.7 ps/gate for 2.5 V at room temperature, which is the fastest CMOS switching ever reported     

A widely tunable narrow linewidth semiconductor fiber ring laser

We have demonstrated a novel approach to obtain a 0.1-nm line width laser with 38-dB sidemode suppression by utilizing a 1.3-μm semiconductor optical amplifier in a fiber unidirectional ring that consists of a linear polarizer and polarization controllers. The laser has a low-threshold current of 22.5 mA as well as a wide tuning range of 28 nm. The new approach is applicable to the 1.55-μm region as well. It is expected that nanosecond wavelength tuning speed is feasible using this approach in conjunction with fast electrooptic polarization controllers, short cavities and low-cavity losses     

Low-threshold tensile-strained InGaAs-InGaAsP quantum-well laserswith single-step separate-confinement heterostructures

The authors studied tensile-strained InGaAs-InGaAsP quantum-well lasers with single-step separate-confinement heterostructures (SCH). They obtained threshold currents below 2 mA at 20°C and below 10 mA at 100°C with indium mole fractions of 0.3 and 0.35 in the active layers. They found that the poorer carrier confinement of the longer wavelength SCH layer lowered the characteristic temperature at high temperatures. A laser with two In_0.35Ga_0.65As wells and a 1.1-μm composition InGaAsP SCH layer produced a 1.6-mA CW threshold current at 20°C and lasing at 120°C. Using this laser, very short lasing delays under zero-bias current over a wide temperature range and 2 Gb/s modulation under zero-bias current at 70°C were achieved