Continuous-wave Threshold Current Research Articles

Distributed feedback lasers using surface gratings in Bragg waveguides.

This Letter presents, to the best of our knowledge, the first report of a narrow-linewidth ∼790-800nm edge-emitting semiconductor distributed feedback Bragg reflection waveguide diode laser (DFB2RL). The DFB2RLs were fabricated using a ridge waveguide structure with 5th order, surface-etched grating forming the wavelength selective element. Unbonded devices with a 500 µm cavity length exhibited continuous wave threshold currents in the region of 25 mA with an output power of 2.5 mW per (uncoated) facet at 100 mA drive current. The devices operated in a single longitudinal mode, with side-mode suppression ratio (SMSR) as high as 49 dB and linewidths as low as 207 kHz. Devices maintained single mode operation with high SMSR over a 9 nm wavelength range as the temperature was swept from 15°C to 50°C.

Low-noise 13 μm InAs/GaAs quantum dot laser monolithically grown on silicon

We report low-noise, high-performance single transverse mode 1.3 μm InAs/GaAs quantum dot lasers monolithically grown on silicon (Si) using molecular beam epitaxy. The fabricated narrow-ridge-waveguide Fabry–Perot (FP) lasers have achieved a room-temperature continuous-wave (CW) threshold current of 12.5 mA and high CW temperature tolerance up to 90°C. An ultra-low relative intensity noise of less than −150 dB/Hz is measured in the 4–16 GHz range. Using this low-noise Si-based laser, we then demonstrate 25.6 Gb/s data transmission over 13.5 km SMF-28. These low-cost FP laser devices are promising candidates to provide cost-effective solutions for use in uncooled Si photonics transmitters in inter/hyper data centers and metropolitan data links.

Monolithic quantum-dot distributed feedback laser array on silicon

Electrically-pumped lasers directly grown on silicon are key devices interfacing silicon microelectronics and photonics. We report here, for the first time, an electrically-pumped, room-temperature, continuous-wave (CW) and single-mode distributed feedback (DFB) laser array fabricated in InAs/GaAs quantum-dot (QD) gain material epitaxially grown on silicon. CW threshold currents as low as 12 mA and single-mode side mode suppression ratios (SMSRs) as high as 50 dB have been achieved from individual devices in the array. The laser array, compatible with state-of-the-art coarse wavelength division multiplexing (CWDM) systems, has a well-aligned channel spacing of 20 0.2 nm and exhibits a record wavelength coverage range of 100 nm, the full span of the O-band. These results indicate that, for the first time, the performance of lasers epitaxially grown on silicon is elevated to a point approaching real-world CWDM applications, demonstrating the great potential of this technology.

490 fs pulse generation from passively mode‐locked single section quantum dot laser directly grown on on‐axis GaP/Si

We demonstrate, for the first time, a single section passively mode-locked InAs/InGaAs quantum dot laser directly grown on on-axis (001) GaP/Si substrate. The laser has a continuous-wave threshold current of 34 mA at 20°C. By forward biasing the laser gain section current at 470 mA, 490 fs pulse generation with 31 GHz repetition rate can be obtained. This simple femtosecond pulse generation structure with CMOS fabrication compatibility makes the laser a promising light source candidate in future large-scale silicon photonic applications.

Perspective: The future of quantum dot photonic integrated circuits

Direct epitaxial integration of III-V materials on Si offers substantial manufacturing cost and scalability advantages over heterogeneous integration. The challenge is that epitaxial growth introduces high densities of crystalline defects that limit device performance and lifetime. Quantum dot lasers, amplifiers, modulators, and photodetectors epitaxially grown on Si are showing promise for achieving low-cost, scalable integration with silicon photonics. The unique electrical confinement properties of quantum dots provide reduced sensitivity to the crystalline defects that result from III-V/Si growth, while their unique gain dynamics show promise for improved performance and new functionalities relative to their quantum well counterparts in many devices. Clear advantages for using quantum dot active layers for lasers and amplifiers on and off Si have already been demonstrated, and results for quantum dot based photodetectors and modulators look promising. Laser performance on Si is improving rapidly with continuous-wave threshold currents below 1 mA, injection efficiencies of 87%, and output powers of 175 mW at 20 °C. 1500-h reliability tests at 35 °C showed an extrapolated mean-time-to-failure of more than ten million hours. This represents a significant stride toward efficient, scalable, and reliable III-V lasers on on-axis Si substrates for photonic integrate circuits that are fully compatible with complementary metal-oxide-semiconductor (CMOS) foundries.

Highly Reliable Low-Threshold InAs Quantum Dot Lasers on On-Axis (001) Si with 87% Injection Efficiency

Quantum dot lasers epitaxially grown on Si are promising for an efficient light source for silicon photonics. Recently, considerable progress has been made to migrate 1.3 μm quantum dot lasers from off-cut Si to on-axis (001) Si substrates. Here, we report significantly improved performance and reliability of quantum dot lasers enabled by a low threading dislocation density GaAs buffer layer. Continuous-wave threshold currents as low as 6.2 mA and output powers of 185 mW have been achieved at 20 °C. Reliability tests after 1500 h at 35 °C showed an extrapolated mean-time-to-failure of more than a million hours. Direct device transparency and amplified spontaneous emission measurements reveal an internal optical loss as low as 2.42 cm–1 and injection efficiency of 87%. This represents a significant stride toward efficient, scalable, and reliable III–V lasers on on-axis Si substrates for photonic integrate circuits that are fully compatible with CMOS foundries.

High efficiency low threshold current 1.3 μm InAs quantum dot lasers on on-axis (001) GaP/Si

We demonstrate highly efficient, low threshold InAs quantum dot lasers epitaxially grown on on-axis (001) GaP/Si substrates using molecular beam epitaxy. Electron channeling contrast imaging measurements show a threading dislocation density of 7.3 × 106 cm−2 from an optimized GaAs template grown on GaP/Si. The high-quality GaAs templates enable as-cleaved quantum dot lasers to achieve a room-temperature continuous-wave (CW) threshold current of 9.5 mA, a threshold current density as low as 132 A/cm2, a single-side output power of 175 mW, and a wall-plug-efficiency of 38.4% at room temperature. As-cleaved QD lasers show ground-state CW lasing up to 80 °C. The application of a 95% high-reflectivity coating on one laser facet results in a CW threshold current of 6.7 mA, which is a record-low value for any kind of Fabry-Perot laser grown on Si.

Watt-Level Room Temperature Continuous-Wave Operation of Quantum Cascade Lasers With λ >10 μm

In this paper, watt-level continuous-wave (CW) output powers at wavelengths longer than 10 μm are demonstrated at room temperature with quantum cascade lasers (QCLs). CW output power of 1.15 W is demonstrated at λ ~ 10.3 μm for a QCL which has a 6-mm-long cavity and a 14-μm-wide stripe. CW output power of 1.3 W is demonstrated at λ ~ 10.7 μm for a QCL which has 6-mm-long cavity and 11.5-μm width, with a CW threshold current of 1.96 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Moreover, 1-W kink-free CW output power is demonstrated with a laser with a 9.5-μm-wide stripe. The maximum pulsed and CW wall plug efficiencies reached 10.4% and 4.8%, respectively, for the QCLs with λ ~ 10.7 μm.

InGaAsP–InP Square Microlasers With a Vertex Output Waveguide

InGaAsP-InP square microlasers with a vertex output waveguide are fabricated by planar processes, and the etched sidewalls of the lasers are confined by insulating layer SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and p-electrode Ti-Au metals. For a square microlaser with a side length of 30 μm and a 2-μm -wide output waveguide, a continuous-wave threshold current is 26 mA at room temperature and output power is 0.72 mW at 86 mA. The mode interval of 21 and 7.4 nm is observed for the microlasers with the side length of 10 and 30 μm , respectively. Finite-difference time-domain (FDTD) simulations indicate that the lasing modes have incident angles of about 45 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> at the boundaries of the resonator. In addition, square resonators surrounded by air, SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Ti-Au, and SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Au are compared by FDTD simulations.

GaAs-based 1.53 µm GaInNAsSb vertical cavity surface emitting lasers

Electrically-pumped GaAs-based 1.53 µm vertical cavity surface emitting lasers operating in pulsed mode at room temperature and continuous wave (CW) up to 20°C are reported for the first time. The lasers employ a GaInNAsSb/GaNAs multiple quantum well active region, a selectively oxidised AlAs aperture and p- and n-doped Al(Ga)As/GaAs distributed Bragg reflectors. Typical devices have room-temperature pulsed threshold current densities of 8.3 kA/cm2 and threshold voltages of 5.5 V. CW threshold currents as low as 2.87 mA for a 7 µm aperture device were observed at 15°C.

Room-temperature continuous-wave operation of the In(Ga)As/GaAs quantum-dot VCSELs for the 1.3 µm optical-fibre communication

Efficient room-temperature (RT) continuous-wave (CW) lasing operation of the 1.3 µm MBE (molecular-beam epitaxy) In(Ga)As/GaAs quantum-dot (QD) top-emitting oxide-confined vertical-cavity surface-emitting diode lasers (VCSELs) for the second-generation optical-fibre communication has been achieved. In their design, a concept of a QD inside a quantum well (QW) has been utilized. The proposed In(Ga)As/GaAs QD active region is composed of five groups of three 8 nm In0.15Ga0.85As QWs, each containing one InAs QD sheet layer. In each group located close to successive anti-node positions of the optical standing wave within the 3λ cavity, QWs are separated by 32 nm GaAs barriers. Besides, at both active-region edges, additional single InGaAs QWs are located containing single QD layers. For the 10 µm diameter QD VCSELs, the RT CW threshold current of only 6.2 mA (7.9 kA cm−2), differential efficiency of 0.11 W A−1 and the maximal output power of 0.85 mW have been recorded. The experimental characteristics are in excellent agreement with theoretical ones obtained using the optical-electrical-thermal-recombination self-consistent computer model. According to this, for the 10 µm devices, the fundamental linearly polarized LP01 mode remains the dominating one up to the current of 9.1 mA. The lowest RT CW lasing threshold below 5 mA is expected for 6 µm devices.

Experimental observation of whispering gallery modes in sector disk lasers

The existence of the whispering gallery modes in a sector disk resonator has been demonstrated theoretically and experimentally observed in a disk, half-disk, and quarter-disk semiconductor lasers. The half-disk and quarter-disk lasers are fabricated from 285μm diameter disks emitted near 2.13μm at room temperature with continuous wave threshold currents of 55–60mA. Mode spacing in emission spectra of the half-disk lasers was the same as for the whole disk and doubled for the quarter disk as expected from the theoretical analysis. Half-disk lasers emit two parallel beams from the cleaved facet, while the two output beams are perpendicular in quarter-disk devices.

Room-temperature continuous-wave operation of GaInNAsSb laser diodes at 1.55 µm

The first 1.55 µm room-temperature continuous-wave (CW) operation of GaAs-based laser diodes utilising GaInNAsSb/GaNAs double quantum well active regions grown by molecular beam epitaxy is reported. In electrically-pumped CW operation the narrow ridge waveguide devices have a room temperature lasing wavelength of 1550 nm near threshold, increasing to 1553 nm at thermal rollover. The CW threshold current was 132 mA for a 3×589 µm device, with a characteristic temperature of 83 K, measured in pulsed mode between 20 and 70°C.

Continuous-wave operation of InGaN multiple quantum well laser diodes grown by molecular beam epitaxy

The first continuous-wave InGaN multiple quantum well laser diodes grown by molecular beam epitaxy are reported. Ridge waveguide lasers are fabricated on free-standing GaN substrates and operated at room temperature under continuous-wave current injection. For 2.2×1000 µm lasers with highly reflective facet coatings a continuous-wave threshold current of 125 mA is obtained, corresponding to a threshold current density of 5.7 kA cm−2. The lasers have a threshold voltage of 8.6 V and lase at a wavelength of ∼405 nm for &gt;3 min at 20°C.

Continuous-wave operation of InGaN multiple-quantum-well laser diodes on copper substrates obtained by laser liftoff

The performance characteristics of continuous-wave (CW) InGaN multiple-quantum-well (MQW) laser diodes on copper substrates are reported. InGaN MQW laser diodes (LDs) grown on sapphire substrates by metal-organic chemical vapor deposition were successfully separated from the sapphire and transferred onto copper substrates by using a two-step laser liftoff (LLO) process. Continuous-wave threshold currents as low as 65 mA have been achieved with threshold voltages of 6.5 V with a backside n-contact through the Cu substrate, improved heat dissipation due to the Cu substrate allowed CW laser operation up to a heatsink temperature of 80/spl deg/C. Significant improvements in light output powers were observed for devices on Cu substrates with maximum CW output power of more than 100 mW.

Edge-emitting microlasers with one active layer of quantum dots

High performance edge-emitting microlasers with deeply etched distributed Bragg reflectors (DBRs) were fabricated on an AlGaAs-GaAs laser structure with a single GaInAs quantum dot (QD) active layer. Mirror reflectivities well above 90% were achieved by third-order narrow air-gap Bragg reflectors with /spl lambda//4 air-gaps. DBR lasers with 160-/spl mu/m-long cavities and cleaved mirrors on one side show differential efficiencies of 0.87 W/A and output powers of more than 50 mW at 980-nm emission wavelength in continuous wave (CW) operation at room temperature. With deeply etched DBRs on both sides of the cavity CW operating microlasers with cavity lengths down to 16 /spl mu/m could be realized with a minimum threshold current of 1.2 mA for a 30-/spl mu/m cavity length. All lasers are emitting at the QD ground state at room temperature. Twenty-/spl mu/m-long devices show CW threshold currents of about 3 mA, output powers above 1 mW, and single mode emission with >25 dB sidemode suppression ratios. First, high-frequency measurements mere performed proving that these QD microlasers are well suited for large-scale integrated high-speed optical data processing with modulation frequencies well above 10 GHz.

High-performance CW 1.26-μm GaInNAsSb-SQW ridge lasers

Long wavelength GaInNAsSb-SQW lasers and GaInAsSb-SQW lasers that include a small amount of Sb were successfully grown by gas-source molecular beam epitaxy (GSMBE). We confirmed that Sb reacts in a highly strained GaInAs-GaAs system and GaInNAs-GaAs system like a surfactant, which increases the critical thickness at which the growth mode changes from two-dimensional (2-D) growth to three-dimensional (3-D) growth. The lasers were processed into ridge lasers. The GaInNAsSb lasers oscillated under continuous-wave (CW) operation at 1.258 /spl mu/m at room temperature. The low CW threshold current of 12.4 mA and high characteristic temperature (T/sub c/) of 157 K were obtained for GaInNAsSb lasers, which is the best result for GaInNAs-based narrow stripe lasers. Further, the GaInNAsSb laser oscillated under CW conditions over 100/spl deg/C. On the other hand, GaInAsSb lasers oscillated under CW operation at 1.20 /spl mu/m at room temperature. The low CW threshold current of 6.3 mA and high characteristic temperature (T/sub c/) of 256 K were obtained for GaInAsSb lasers, which is also the best result for 1.2-/spl mu/m-range highly strained GaInAs-based narrow stripe lasers. We can say that GaInNAsSb lasers are very promising material for realizing an access network. Further, the differential gain of GaInNAs-based SQW lasers was estimated for the first time. GaInNAsSb-SQW lasers have the extremely large differential gain of 1.06-10/sup -15/ cm/sup 2/ in spite of the single-QW lasers; therefore, GaInNAsSb lasers are also suitable for high-speed lasers in the long wavelength region.

Low-threshold oxide-confined GaInNAs long wavelength vertical cavity lasers

We report, for the first time, room temperature continuous-wave (CW) operation of GaInNAs vertical-cavity surface-emitting laser diodes emitting at a wavelength of 1.2 μm and grown all-epitaxially in a single step on a GaAs substrate. Oxide-apertured devices demonstrated CW threshold currents as low as 1 mA, slope efficiency above 0.045 W/A, and thermal impedance of 1.24 K/mW. Larger sized devices exhibited a pulsed threshold current density of 2-2.5 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and slope efficiency above 0.09 W/A.

All selective metalorganic vapor phase epitaxy grown buried-heterostructure laser diodes with selectively oxidized AlInAs current-confinement layer

A laser diode structure, consisting of a 1.3 μm all selective metalorganic vapor phase epitaxy grown buried-heterostructure (ASM-BH) laser diode with a selectively oxidized-AlInAs current-confinement layer, is proposed and demonstrated. As the lateral oxidization is automatically stopped near the active layer by self-aligned AlInAs, a narrow current aperture with excellent controllability is realized. The fabricated laser diode shows low continuous-wave threshold current of 2.5 and 7.5 mA at 25 and 85 °C, respectively, for 250-μm-long devices with HR(75%)/HR(95%) coatings. The maximum operating temperature is higher than 145 °C.

Low-threshold continuous-wave two-stack quantum-dot laser with reduced temperature sensitivity

Data are presented on continuous wave operation of two-stack quantum dot lasers designed with reduced temperature sensitivity in their threshold. The InAs quantum dots are designed to have a wide energy spacing (/spl sim/102 meV) between the ground and first excited radiative transitions. Selectively oxidized stripe lasers have continuous wave threshold currents as low as 1.2 mA for 2 μm wide stripes and minimum threshold current densities of 26 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for 13-μ-m wide stripes. Broad area lasers have continuous wave threshold current densities as low as 40 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , even for p-up mounting. Ground state lasing is obtained up to the highest temperature measured of 326 K.