Wavelength tunable distributed Bragg reflector laser integrated with electro-absorption modulator by a combined method of selective area growth and quantum well intermixing - art. no. 68240N

Wavelength tunable electro-absorption modulated distributed Bragg reflector lasers (TEMLs) are promising light source in dense wavelength division multiplexing (DWDM) optical fiber communication system due to high modulation speed, small chirp, low drive voltage, compactness and fast wavelength tuning ability. Thus, increased the transmission capacity, the functionality and the flexibility are provided. Materials with bandgap difference as large as 250nm have been integrated on the same wafer by a combined technique of selective area growth (SAG) and quantum well intermixing (QWI), which supplies a flexible and controllable platform for the need of photonic integrated circuits (PIC). A TEML has been fabricated by this technique for the first time. The component has superior characteristics as following: threshold current of 37mA, output power of 3.5mW at 100mA injection and 0V modulator bias voltage, extinction ratio of more than 20 dB with modulator reverse voltage from 0V to 2V when coupled into a single mode fiber, and wavelength tuning range of 4.4nm covering 6 100-GHz WDM channels. A clearly open eye diagram is observed when the integrated EAM is driven with a 10-Gb/s electrical NRZ signal. A good transmission characteristic is exhibited with power penalties less than 2.2 dB at a bit error ratio (BER) of 10(-10) after 44.4 km standard fiber transmission.

Control of the photonic crystal waveguide over the beam profile of vertical-cavity surface-emitting lasers

The control of the photonic crystal waveguide over the beam profile of vertical-cavity surface-emitting lasers is investigated. The symmetric slab waveguide model is adopted to analyze the control parameters, of the beam profile in the photonic-crystal vertical-cavity surface-emitting laser (PC-VCSEL). The filling factor (the ratio of the hole diameter to the lattice constant) and the etching depth control the divergence angle of the PC-VCSEL, and the low filling factor and the shallow etching depth are beneficial to achieve the low-divergence-angle beam. Two types of PC-VCSELs with different filling factors and etching depths are designed and fabricated. The experimental results show that the device with a lower filling factor and a shallower etching depth has a lower divergence angle, which agrees well with the theoretical predictions.

Temperature-dependent modulation characteristics for 1.3 mu m InAs/GaAs quantum dot lasers

Temperature-dependent modulation characteristics of 1.3 mu m InAs/GaAs quantum dot (QD) lasers under small signals have been carefully studied at various bias currents. Based on experimental observations, it is found that the modulation bandwidth significantly increases when excited state (ES) lasing emerges at high temperature. This is attributed to additional photons emitted by ES lasing which contribute to the modulation response. A rate equation model including two discrete electron energy levels and the level of wetting layer has been used to investigate the temperature-dependent dynamic behavior of the QD lasers. Numerical investigations confirm that the significant jump for the small signal modulation response is indeed caused by ES photons. Furthermore, we identify how the electron occupation probabilities of the two discrete energy levels can influence the photon density of different states and finally the modulation rate. Both experiments and numerical analysis show that the modulation bandwidth of QD lasers at high temperature can be increased by injecting more carriers into the ES that has larger electron state degeneracy and faster carrier's relaxation time than the ground state.

Self-heating effect in 1.3 mu m p-doped InAs/GaAs quantum dot vertical cavity surface emitting lasers

The self-heating effect in 1.3 mu m p-doped InAs/GaAs quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) has been investigated using a self-consistent theoretical model. Good agreement is obtained between theoretical analysis and experimental results under pulsed operation. The results show that in p-doped QD VCSELs, the output power is significantly influenced by self-heating. About 60% of output power is limited by self-heating in a device with oxide aperture of 5x6 mu m(2). This value reduces to 55% and 48%, respectively, as the oxide aperture increases to 7x8 and 15x15 mu m(2). The temperature increase in the active region and injection efficiency of the QDs are calculated and discussed based on the different oxide aperture areas and duty cycle.

Broadband external cavity tunable quantum dot lasers with low injection current density

Broadband grating-coupled external cavity laser, based on InAs/GaAs quantum dots, is achieved. The device has a wavelength tuning range from 1141.6 nm to 1251.7 nm under a low continuous-wave injection current density (458 A/cm(2)). The tunable bandwidth covers consecutively the light emissions from both the ground state and the 1st excited state of quantum dots. The effects of cavity length and antireflection facet coating on device performance are studied. It is shown that antireflection facet coating expands the tuning bandwidth up to similar to 150 nm, accompanied by an evident increase in threshold current density, which is attributed to the reduced interaction between the light field and the quantum dots in the active region of the device.

Self-Heating Effect on the Two-State Lasing Behaviors in 1.3-mu m InAs-GaAs Quantum-Dot Lasers

Experimental and theoretical study of the self-heating effect on the two-state lasing behaviors in 1.3-mu m self-assembled InAs-GaAs quantum dot (QD) lasers is presented. Lasing spectra under different injected currents, light-current (L-I) curves measured in continuous and pulsed regimes as well as a rate-equation model considering the current heating have been employed to analyze the ground-state (GS) and excited-state (ES) lasing processes. We show that the self-heating causes the quenching of the GS lasing and the ES lasing by the increased carrier escape rate and the reduced maximum modal gain of GS and ES.

OPTICAL CHARACTERISTICS OF GAAS/ALGAAS RIDGE-QUANTUM-WELL-WIRES GROWN BY MBE ON NONPLANAR SUBSTRATES

With conventional photolithography and wet chemical etching, we have realized GaAs/AlGaAs buried ridge-quantum-well-wires (RQWWs) with vertically stacked wires in lateral arrays promising for device application, which were grown in situ by a single-step molecular beam epitaxy growth and formed at the ridge tops of mesas on nonplanar substrates. Confocal photoluminescence (CPL) and polarization-dependent photoreflectance (PR) are applied to study optical characteristics of RQWWs. Lateral bandgap modulation due to lateral variation of QW layer thickness is demonstrated not only by CPL but also by PR. As one evidence for RQWWs, a large blue shift is observed at the energy level positions for electronic transitions corresponding to quantum wells (QWs) at the ridge tops of mesas compared with those corresponding to QWs on nonpatterned areas of the same sample. The blue shift is in contradiction with the fact that the GaAs QW layers at the tops of the mesas are thicker than those on nonpatterned areas. The other evidence for RQWWs, optical anisotropy is provided by the polarization-dependent PR, which results from lateral quantum size effect existing at the tops of the mesas.

GAAS/GAALAS GRADED INDEX SEPARATE CONFINEMENT SINGLE QUANTUM-WELL SINGLE-MODE WAVE-GUIDE ELECTROABSORPTION LIGHT-MODULATOR

A GaAs/GaAlAs graded-index separate confinement single quantum well heterostructure single-mode ridge waveguide electroabsorption modulator was fabricated and investigated. For the modulator with a quantum well width of 100 angstrom and device length of 700-mu-m, an on/off ratio of 29.7 dB and estimated absorption insertion loss of 3 dB were obtained for TE polarised light with wavelength 8650 angstrom, and for TM polarisation the on/off ratio was 28.5 dB. With a switching voltage of 1 V, an on/off ratio of 15 dB was achieved. Photocurrent spectra exhibited a red shift of 600 angstrom of the absorption edge when the voltage applied to the PIN diode was varied from 0.5 to -7 V. The corresponding shift of the room temperature exciton peak energy was 96 meV.

ENHANCEMENT EFFECT OF PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITED SIN CAPPING LAYER ON DIELECTRIC CAP QUANTUM-WELL DISORDERING

Quantum well disordering of GaAs/AlGaAs multiple quantum well(MQW) has been accomplished with only plasma enhanced chemical vapor deposited (PECVD) SiN cap layer growth. The amount of blue shift increases with SiN growing time. This result has been explained by the vacancy indiffusion during PECVD SiN growth. Rapid thermal annealing (RTA) of the sample after SiN cap layer growth at 850 degrees C for 35 s caused a larger amount of blue shift than those obtained without RTA. By considering the model of Al diffusion from AlGaAs barrier into GaAs QWs together with the result from photoluminescence (PL) measurement, Al diffusion coefficients were calculated. The Al diffusion coefficient due to PECVD SiN was estimated at about 3 x10(-17) cm(2)/s. It was possible to extract the effect of RTA on the QW disordering, which showed that the amount of the blue shift and the Al diffusion coefficient due only to RTA increases with SiN cap layer thickness as reported by Chi et al.(10))

PULSED ELECTRICAL OPERATION OF 1.5-MU-M VERTICAL-CAVITY SURFACE-EMITTING LASERS

Vertical cavity surface emitting lasers operating in the 1.3- and 1.5-mu m wavelength ranges are highly attractive for telecommunications applications. However, they are far less well-developed than devices operating at shorter wavelengths. Pulsed electrically-injected lasing at 1.5 mu m, at temperatures up to 240 K, is demonstrated in a vertical-cavity surface-emitting laser with one epitaxial and one dielectric reflector. This is an encouraging result in the development of practical sources for optical fiber communications systems.

Self-aligned Coupled Waveguide Distributed Bragg Reflector Lasers

A novel self-aligned coupled waveguide (SACW) multi-quantum-well (MQW) distributed Bragg reflector (DBR) laser is proposed and demonstrated for the first time. By selectively removing the MQW layer and leaving the low SCH/SACW layer the Bragg grating is partially formed on this layer. By optimizing the thickness of the low SCH/SACW layer, a ～80% coupling efficiency between the MQW gain region and the passive region are obtained. The typical threshold current of the SACW DBR laser is 39 mA, the slope efficiency can reach to 0.2 mW/mA and the output power is more than 20 mW with a more than 30dB side mode suppression ratio.

Measurement of Cavity Loss and Quasi-Fermi-Level Separation for Fabry-Perot Semiconductor Lasers

A fitting process is used to measure the cavity loss and the quasi-Fermi-level separation for Fabry- Perot semiconductor lasers. From the amplified spontaneous emission (ASE) spectrum, the gain spectrum and single-pass ASE obtained by the Cassidy method are applied in the fitting process. For a 1550nm quantum well InGaAsP ridge waveguide laser, the cavity loss of about ～24cm~(-1) is obtained.

Tunable MQW-DBR lasers using selective area growth

The tunable ridge waveguide distributed Bragg reflector (DBR) lasers designed for wavelength-division-multiplex (WDM) communication systems at 1.55 um by using selective area growth (SAG) is reported. The threshold current of the DBR laser is 62mA and the output power is more than 8mW. The isolation resistance between the active region and the Bragg region is 30K Ohm. The total tuning range is 6.5nm and this DBR laser can provide 6 continuous standard WDM channels with 100GHz channel spacing; in the tuning range, the single mode suppression ratio (SMSR) is maintained more than 32dB and the maximum output power variation is less than 3dB.

High temperature operation of 650nm AlGaInP quantum well laser diodes grown by LP-MOCVD

Low threshold current and high temperature operation of 650nm AlGaInP quantum well laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) are reported in this paper. 650nm laser diodes with threshold current as low as 22-24mA at room temperature, and the operating temperature over 90 degrees C at CW output power 5 mW were achieved in this study. These lasers are stable during 72 hours burn in under 5mW at 90 degrees C.

High performance 1.55 mu m InGaAsP/InP strained layer quantum well laser diodes fabricated by MOCVD overgrowth method

High performance uncooled 1.55 mu m InGaAsP/InP strained layer quantum well (SL-QW) lasers grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) were reported in this paper. Whole MOCVD over growth method were applied in this work. The threshold currents of 5mA and the highest lasing temperature of 122 degrees C were obtained.