Stable CW Operation Research Articles

High-power, stable single-mode CW operation of 1550 nm wavelength InP-based photonic-crystal surface-emitting lasers

1550 nm wavelength photonic-crystal surface-emitting lasers (PCSELs) are attractive for optical communication and eye-safe sensing applications. In this study, we present InP-based PCSELs featuring a double-lattice photonic-crystal structure designed for high-power single-mode operation at a wavelength of 1550 nm. These PCSELs demonstrate output powers exceeding 300 mW under continuous-wave conditions at 25 °C. Additionally, highly stable single-mode oscillation with a side-mode suppression ratio of over 60 dB is verified at temperatures from 15 °C to 60 °C. Measurement and simulation of photonic band structures reveal the impacts of the threshold gain margin and optical coupling coefficient on the single-mode stability.

RF and thermal studies on conduction cooled Nb3Sn SRF cavity

Advancements in the development of Nb3Sn coatings for superconducting radio-frequency (SRF) cavities have enabled efficient RF operation at 4.2 K. This has made the use of new cooling methods possible, namely those based on conduction cooling from commercial cryocoolers. Using cryocoolers in place of liquid helium as a cooling source eliminates the need for expensive and complex cryogenic infrastructure, making SRF technology accessible to small-scale applications in fields such as medicine, industry, environmental sustainability and more. At Cornell University, we have developed a new cavity testing assembly which uses a Cryomech PT420-RM cryocooler to cool a 2.6 GHz Nb3Sn cavity. We have performed several rounds of RF and diagnostic testing using this new assembly. Our best results demonstrated stable CW operation at 10 MV/m, with the cavity remaining at 4.2 K or lower. This represents breakthrough performance for a conduction cooled cavity, in which accelerating gradients relevant to some industrial applications were achieved. Our analysis highlights the importance of reducing thermal gradients across the cavity during cooldown; different methods for achieving this were successfully developed and demonstrated. We also found close agreement regarding thermal behavior between experimental measurements and numerical simulations, validating our chosen conduction cooling methods and providing guidance for future improvements. These findings will serve as a foundation for designing a new cryocooler-based cryomodule which will provide beam energy gains on the order of 1 MeV for beam currents up to 100 mA.

RF power tests of rf input coupler for the IFMIF/EVEDA RFQ prototype linac

For the IFMIF/EVEDA accelerator prototype RFQ linac, a 175MHz rf input coupler based on a 6 1/8in. co-axial waveguide is designed and manufactured. The rf coupler has cooling channels into the loop antenna and inner/outer-conductors around the RF window for CW operation mode, and the rf vacuum window module is replaceable by flanged connection. For rf power capability, nominal rf power of 160kW and maximum transmitted rf power of 200kW are required. In order to test the rf power capability, rf power tests using a high-voltage standing waves on a high-Q load circuit are carried out. For manufactured nine rf couplers including one spare, a stable 14s CW operation at the equivalent rf power of 200kW were achieved within 3–5days rf aging. No rf contact defects, no unnecessary low-Q value and no extraordinary outgassing were validated.

High optical strength GaAs-based laser structures

The optical-strength properties of 3S PHOTONICS GaAs-based semiconductor laser structures are presented. After some general considerations about this robustness issue, typical of high-power diode lasers, the performances in both CW and pulsed current injection of our best vertical structures are presented and it is shown that our current generation of 980nm laser diodes can withstand very high facet temperatures (180–200°C) in stable CW operation. Thus, we demonstrate a large margin between the facet temperature in operation conditions and the observed maximum critical value. Maximum CW saturation powers exceeding 3W from a single-lateral mode device have been obtained with the longest laser cavities (7.5mm) at around 5A. Also, very high peak powers are demonstrated in pulsed current experiments opening the way to new specific applications, using available production devices. Specific degradation patterns after high peak current single-pulse induced damage have been observed by cathodo-luminescence imaging and are also discussed. Finally, comparisons between devices emitting at 980nm and 1060nm are considered.

A CW, polarization-maintaining .LAMBDA./4-shifted DFB Er-doped fiber laser at 1.54.MU.m

We describe a polarization-maintaining (PM) λ/4-shifted DFB Er-doped fiber laser (EDFL), in which optical pulsation effects caused by Er3+ ion-pairs were successfully removed by co-doping erbium fiber with 12wt% aluminum. Stable CW operation was realized at a pump power of 100mW. The laser exhibited single longitudinal-mode oscillation with a single polarization. The output power, linewidth of the longitudinal mode, and RIN at the relaxation oscillation frequency were 0.5mW, 82kHz, and -79dB/Hz at a pump power of 100mW, respectively. Stable operation was also obtained at a pump power of 140mW, where the above values were improved to 0.8mW, 43kHz, and -92dB/Hz, respectively.

Stable CW operation of field-plated GaN-AlGaN MOSHFETs at 19 W/mm

We report for the first time the dc and radio frequency (RF) operation of a field-plated GaN-AlGaN metal-oxide-semiconductor heterostructure field effect transistor (MOSHFET). At 2 GHz and an RF output power level of 19 W/mm (drain bias 55 V), the device exhibited a remarkably stable operation for times in excess of 100 h. In contrast, a similar geometry HFET from the same wafer continuously degraded from 17 W/mm down to 14 W/mm within the first 20 h. We attribute the stable performance of the MOSHFET at high microwave powers to the extremely low gate-leakage currents and the current collapse-free operation resulting from the field-plated design.

Direct current H− source for the medicine accelerator (invited)

A compact cw hydrogen negative ion source having reliable operation and a simplified maintenance is developed at Budker Institute of Nuclear Physics for a tandem accelerator of boron capture neutron therapy installation. The source uses a Penning discharge with a hydrogen and cesium feed through the hollows in the cathodes. Discharge voltage is about 60–80 V, current 9 A, hydrogen pressure 4–5 Pa, magnetic field 0.05–0.1 T, and cesium seed <1 mg/h. Negative ions are mainly produced on the cesiated anode surface due to conversion of hydrogen atoms. An optimal anode temperature is 250–350 °C. Negative ion beam current is directly proportional to the discharge current and to the emission hole area. A triode system for the beam extraction and acceleration system is used. The flux of accompanying extracted electrons was decreased by filtering in the transverse magnetic field. This electron flux was intercepted to the special electrode, biased at 4 kV potential with respect to the anode. Source stable cw operation for several hour runs was multiply tested. A H− ion beam with current up to 8 mA, beam energy 23 keV was produced regularly. Negative ion current of heavy impurities had a value of about 3% of the total beam current. Beam normalized emittance is about 0.3 π mm mrad and emission current density −0.1 A/cm2. A built-in cathode heater provides the operation quick start.

Kinetics of a solid-state laser with polarizable saturable absorber

In this work we present a numerical study of a three-level laser containing a polarizable saturable absorber inside the cavity. This model allows us to study the kinetics of solid-state lasers in a general form. The stability of Q-switching regime is analyzed by means of numerical solution of rate equations; and main results of our analysis let us suggest that under certain conditions, the laser may pass from unstable relaxation oscillations to a stable CW operation by changing the mutual orientation of the absorber and polarizer, or by choosing the pump level.

Suppression of self-pulsing behavior in erbium-doped fiber lasers with resonant pumping: experimental results

Experimental results are presented showing that resonant pumping can significantly improve the stability of erbium-doped fiber lasers. In particular, it is observed that an erbium fiber laser that exhibits sustained spiking behavior when pumped at 980 nm will revert to stable cw operation when pumped at 1510 nm.

Stable CW operation of 1.3 µm double-heterostructurelaser heteroepitaxially grown on Si

Stable CW operation for over 800 h at 25°C is demonstrated for the first time for a 1.3 µm DH LD heteroepitaxially grown on Si. This is attributable to the high performance of the LDs, approaching that of similar LDs grown on InP.

Very high-power-density CW operation of GaAs/AlGaAs microwave heterojunction bipolar transistors

Thermal instability of multi-emitter high-power microwave heterojunction bipolar transistors (HBTs) was eliminated using a novel heat spreading technique that regulates internal device currents to avoid the formation of hot spots. Devices with 2- and 3- mu m minimum emitter sizes and no intentional ballast resistors showed unconditionally stable CW operation up to the device electronic limitations. A record 10-mW/ mu m/sup 2/ power density was obtained at 10 GHz with 7-dB gain and 60% power-added efficiency. The highest efficiency was 67.2% at 9.3-mW/ mu m/sup 2/ power density. It was shown that stable high-power-density operation can be maintained at multiwatt output power levels.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High temperature (77 °C) operation of 634 nm InGaAlP multiquantum-well laser diodes with tensile-strained quantum wells

634 nm InGaAlP multiquantum-well (MQW) laser diodes, with tensile-strained InGaP well layers, have been investigated. A threshold current as low as 59 mA was achieved, at 20 °C, under continuous wave (cw) operation. These MQW laser diodes were able to operate up to temperatures as high as 77 °C under cw conditions. This maximum cw operation temperature is the highest ever reported for 634 nm laser diodes. These MQW laser diodes have shown stable cw operation over 2000 h at an output power of 3 mW, at an ambient temperature of 50 °C.

150 mW fundamental-transverse-mode operation of 670 nm window laser diode

Fundamental-transverse-mode high-power CW operation over 150 mW has been realized in AlGaInP/GaInP 670-nm window laser diodes. A window structure of Zn-induced-disordered GaInP has been fabricated by solid phase diffusion using ZnO film. A compressively strained double-quantum-well active layer and a multiple quantum barrier (MQB) also have been employed for reduction of threshold current. Stable CW operation beyond 1500 h has been observed under 50 mW at 50 degrees C.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Strained Single-Quantum-Well AlGaInP Laser Diodes with Asymmetric Waveguiding Structure

The strained single-quantum-well AlGaInP laser diodes reported here can operate at high output powers and high temperatures through the use of asymmetric waveguiding structures (AWS). By examining the dependence of the laser characteristics on the strain, we first determined the appropriate amount of the strain to be introduced in the active layer. Introducing the AWS into the strained single-quantum-well lasers then reduced their internal optical loss from 14.6 to 8.8 cm-1 by shifting the beam profile peak. In addition, the associated reduction of the optical absorption in the waveguide decreased the threshold current by about 30% and increased the maximum output power by about 50%. As a result, a 60 mW stable CW operation at a wavelength of 690 nm is attained at temperatures as high as 90°C.

Stable cw operation at room temperature of a 1.5-μm wavelength multiple quantum well laser on a Si substrate

Room-temperature cw operation of an InGaAs/InGaAsP multiple quantum well (MQW) laser diode on a Si substrate is reported. The MQW laser emits at a 1.54 μm wavelength and exhibits no degradation after over 2000 h of operation. Employing a hybrid organometallic vapor phase epitaxy/vapor mixing epitaxy method and a layer structure for improving crystalline quality, high-quality MQW layers are obtained. A stable longitudinal mode spectrum demonstrates the effectiveness of the MQW active layer.

High-temperature operation of high-power InGaAlP visible light laser diodes with an In0.5+δGa0.5−δP active layer

High-power and high-reliable operation of transverse-mode stabilized InGaAlP laser diodes has been achieved by a selectively buried ridge waveguide structure with a thin (0.02 μm) active layer. A composition-shifted In0.5+δGa0.5−δP active layer was employed in order to improve the temperature characteristic. A maximum cw light output power of 54 mW was obtained for the laser with antireflection and high-reflection coatings. A high-power cw operation above 30 mW output power was maintained even at a 60 °C heat-sink temperature. Stable cw operation exceeding 1000 h has been achieved for 20 mW output power at 50 °C.

Stable CW operation of a MQW laser emitting at 1.54 mu m on a Si substrate at room temperature

Summary form only given. The MQW laser exhibits no degradation during 500 h of CW operation. Employing a hybrid organometallic vapor-phase epitaxy/vapor-phase epitaxy method, high-quality InP films with a full width at half maximum for the X-ray rocking curve of 110 arcsec, a dislocation density of 10/sup 7/ cm/sup -2/, and low residual stress of 2*10/sup 8/ dyn/cm/sup 2/ were obtained. Results of a preliminary CW aging test at room temperature showed no operational degradation over 500 h with a constant output power of 2 mW per facet. This LD appears to be a promising light source candidate for application to OEICs (optoelectronic integrated circuits). >

Low temperature-stressed aging test of 1.3–1.45 μm laser diodes under high power operation

Maximum CW output powers of 380 and 300 mW were obtained from LDs at 1.3 and 1.45 μm, respectively, at a temperature of ―40 o C. Temperature-stressed CW aging tests were carried out under high output powers of about 260 mW at 1.3 μm and 220 mW at 1.45 μm. The degradation rates of output power were estimated to be less than 3% per 1000 h from the 1600 h aging tests. Stable CW operation has been confirmed under extremely high power operation at low temperature

Visible laser diodes grown by molecular beam epitaxy.

High-quality AlGaInP lavers lattice-matched to a GaAs substrate have successfully been grown by solid source MBE with a dimeric phosphorus beam. The bulk crystal quality and the abruptness of heterointerfaces were studided by measuring a photoluminescence spectrum. Net acceptor concentration in Be doped AlInP reaches saturation above -1×1018 cm-3. A 10-μm wide stripe-geometry GaInP/AlInP laser diode is capable of stable CW operation at room temperature. The maximum output power of 12 mW was achieved.

Operating characteristics and elevated temperature lifetests of focused ion beam micromachined transverse junction stripe lasers

The operating characteristics of transverse junction stripe diode lasers with focused ion beam micromachined mirrors are shown to be comparable to those with cleaved facet mirrors. Stable cw operation for more than 2200 h was observed in an aging test at 55 °C.