Cryogenic operation of AlGaAs-GaAs vertical-cavity surface-emitting lasers at temperatures from 200 K to 6 K

We demonstrate for the first time the CW performance of AlGaAs-GaAs vertical-cavity surface-emitting lasers (VCSELs) at cryogenic temperatures from 6 K to 200 K. By detuning the cavity mode with respect to the gain peak so that optimum dc lasing operation is achieved at -100 K, we find that this optimum lasing performance can be maintained down to temperatures as low as 6 K. Across a broad range of temperatures from 200 K to 6 K, the minimum threshold current of a 16-/spl mu/m diameter VCSEL stayed below 4 mA, while its -3-dB modulation bandwidth increased by about 70% to 11 GHz at 6 K, and the external slope efficiency is greater than 70%.     

Cryogenic VCSELs with chirped multiple quantum wells for a very wide temperature range of CW operation

Cryogenic optical data links require an efficient optical source with temperature-insensitive continuous-wave (CW) operation at low temperatures. Also, to simplify optical alignment, it is desirable to obtain CW operation over a broad temperature range that spans both the low and high temperatures. By the use of vertical-cavity surface-emitting lasers (VCSELs) with chirped (nonuniform) multiple quantum wells (MQWs) to broaden the optical gain spectrum, CW operation has been achieved from 5-350 K, with improved characteristics in both the high- and low-temperature regimes. In particular, temperature-insensitive, submilliampere threshold current was achieved at temperatures from 5-50 K, with a threshold current density of 350 A/cm/sup 2/, and a threshold voltage that is below 3 V.     

Efficient double intracavity-contacted vertical-cavitysurface-emitting lasers with very low-threshold and low-powerdissipation designed for cryogenic applications

Efficient continuous wave operation of oxide-confined double intracavity-contacted InGaAs-GaAs vertical-cavity surface-emitting lasers (VCSEL's) with low-threshold voltage, low-threshold current and low-power dissipation has been achieved over a wide range of cryogenic temperatures (77 K-250 K). Low operating voltages were obtained by routing current through two intracavity contacts to bypass both distributed Bragg reflector (DBR) mirrors, while lower optical losses were achieved by using undoped DBR mirrors with abrupt heterointerfaces. This resulted in low operating voltages (<1.5 V), submilliampere threshold currents (I_th~0.15 mA), low-power dissipation (~0.21 mW at threshold) and a high power conversion efficiency (η _eff=31%)     

Low-temperature optimized vertical-cavity lasers with submilliamp threshold currents over the 77-370 K temperature range

We demonstrate an extended temperature range (77-370 K) of continuous wave (CW) operation for dielectrically-apertured double-intracavity-contacted vertical-cavity InGaAs strained QW lasers optimized for operation at cryogenic temperatures. Superior performance is achieved through the alignment of the cavity mode with the gain of the first and second quantized subbands at 77 K and room temperature, respectively. This design results in submilliamp threshold currents over a 77-370 K temperature range for 5.4-/spl mu/m diameter lasers. The threshold is 120 /spl mu/A and the output power is >8 mW at 77 K.     

Vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots

Molecular beam epitaxy-grown 0.98-/spl mu/m vertical-cavity surface-emitting lasers (VCSELs) with a three-stack submonolayer (SML) InGaAs quantum-dot (QD) active region and fully doped Al/sub x/Ga/sub 1-x/As-GaAs DBRs was studied. Large-aperture VCSELs demonstrated internal optical losses less than 0.1% per one pass. Single-mode operation throughout the whole current range was observed for SML QD VCSELs with the tapered oxide apertures diameter less than 2 /spl mu/m. Devices with 3-/spl mu/m tapered-aperture showed high single-mode output power of 4 mW and external quantum efficiency of 68% at room temperature.     

Selectively etched tunnel junction for lateral current and optical confinement in InP-based vertical cavity lasers

We demonstrate a thin, selectively lateral-etched, AlIn(Ga)As tunnel-junction (TJ) layer as a current and optical confinement aperture in the InP-based long-wavelength vertical cavity surface-emitting lasers (VCSELs). A high etch selectivity was demonstrated by etching the aperture a distance of several microns without affecting the surrounding InP etch-resistant layer. Edgeemitting lasers enclosing the TJ aperture showed high injection efficiency and low current spreading underneath the aperature. Single-mode continuous-wave operation of a 1.55-μm VCSEL was demonstrated successfully with a room-temperature differential efficiency of 21% using a 6-μm-wide TJ aperature.     

Degradation-robust 850-nm vertical-cavity surface-emitting lasers for 25Gb/s optical data transmission

Highly efficient fast vertical-cavity surface-emitting lasers (VCSELs) for the 850-nm spectral range, promising for the development of optical interconnections with a data transmission rate of 25 Gbit/s per channel, are fabricated and studied. Lasers with a selectively oxidized current aperture 6 μm in diameter demonstrate multimode lasing with a quantum efficiency of 35–45% and a threshold current of 0.5–0.7 mA in the temperature range 20–85°C. According to the results of small-signal frequency analysis, the maximum modulation frequency of the lasers exceeds 17 GHz, with the rate of its increase with current exceeding 9 GHz/mA^1/2, which provides VCSEL operation at a rate of 25 Gbit/s in the entire working temperature range. Endurance tests for 3000 h did not reveal any sudden degradation of the lasers. The optical power at working point and the threshold current changed relative to that at the beginning of the tests by no more than 5 and 10%, respectively.     

Power minimization and technology comparisons for digitalfree-space optoelectronic interconnections

This paper investigates the design optimization of digital free-space optoelectronic interconnections with a specific goal of minimizing the power dissipation of the overall link, and maximizing the interconnect density. To this end, we discuss a method of minimizing the total power dissipation of an interconnect link at a given bit rate. We examine the impact on the link performance of two competing transmitter technologies, vertical cavity surface emitting lasers (VCSELs) and multiple quantum-well (MQW) modulators and their associated driver-receiver circuits including complementary metal-oxide-semiconductor (CMOS) and bipolar transmitter driver circuits, and p-n junction photodetectors with multistage transimpedance receiver circuits. We use the operating bit-rate and on-chip power dissipation as the main performance measures. Presently, at high bit rates (>800 Mb/s), optimized links based on VCSELs and MQW modulators are comparable in terms of power dissipation. At low bit rates, the VCSEL threshold power dominates. In systems with high bit rates and/or high fan-out, a high slope efficiency is more important for a VCSEL than a low threshold current. The transmitter driver circuit is an important component in a link design, and it dissipates about the same amount of power as that of the transmitter itself. Scaling the CMOS technology from 0.5 μm down to 0.1 μm brings a 50% improvement in the maximum operating bit rate, which is around 4 Gb/s with 0.1 μm CMOS driver and receiver circuits. Transmitter driver circuits implemented with bipolar technology support a much higher operating bandwidth than CMOS technology; they dissipate, however, about twice the electrical power. An aggregate bandwidth in excess of 1 Tb/s-cm² can be achieved in an optimized free-space optical interconnect system using either VCSELs or MQW modulators as its transmitters     

Fabrication of low-threshold red VCSELs

Red vertical cavity lasers (VCSELs) are ideally suited as optical sources for plastic optical fibre networks. These networks will form the communication backbone of future automobiles and aircraft replacing the current copper networks. However VCSELs at these wavelengths are difficult to realise due to the lower refractive index offsets and unsuitable band structure alignments. The Esprit BREDSELS project has addressed the design, growth and fabrication of low threshold red VCSELs. This paper reports the fabrication of record low threshold (200 μA at 20°C) VCSELs at a wavelength of 665 nm. This device performance has been achieved through the use of selective oxidation techniques. The devices operate CW to 50°C. The trade off between low threshold and high power will be discussed.     

Silicon oxide-planarized single-mode 850-nm VCSELs with TO package for 10 Gb/s data transmission

In this letter, we report on an alternative method to fabricate a high-efficiency planar-type oxide-confined 850-nm vertical-cavity surface-emitting lasers (VCSELs). The planarized process of VCSELs was to use the silicon oxide as the buried layer. As a result, these devices with an oxidized aperture of 3 /spl mu/m in diameter exhibit a single-transverse mode behavior throughout the operation current range. In addition, the static characteristics of VCSELs at 300 K include a threshold current of 0.52mA corresponding to a threshold voltage of 2.2 V, a maximum single transverse-mode light output power of 1.13 mW at 4.5 mA, and an external differential quantum efficiency of 35%. On the other hand, this TO-packaged planar-type 850-nm VCSEL for back-to-back test shows a wide open along with symmetric eye diagram and could also pass the 10 Gb/s mask as operating at 10.3 Gb/s and 4 mA. Furthermore, the VCSEL can still keep the eye diagram open and symmetric after the 66-m multi-mode fiber transmission and has a power penalty of 6.6 dB because of fiber dispersion for 10.3 Gb/s data rate at a bit error rate of 10/sup -11/. These results confirm the excellent high-speed performance of SiO/sub x/-planarized VCSELs as compared to the polyimide-planarized VCSELs.     

High-efficiency and high-power vertical-cavity surface-emittinglaser designed for cryogenic applications

We report the first AlGaAs-GaAs vertical-cavity surface-emitting laser (VCSEL) that has been optimized for cryogenic applications near 77 K, with superior characteristics that include a high-output power (P_out=22 mW at I=25 mA), high power conversion efficiency (ηd=32%), low threshold voltage (V_th=1.75 V) and current (I_th=1.7 mA), and low power dissipation (9 mW at P_out =2.0 mW) for a 20-μm-diameter device     

L 波段宽带低温低噪声放大器的设计与测量*

高电子迁移率晶体管(HEMT)的小信号等效电路低温模型是研制致冷低噪声放大器(LNA)与研究晶 体管微波特性的基础。该文通过测量HEMT 器件在低温环境下直流参数与散射参数(S 参数),构建了包含噪声参 量的小信号等效电路,并据此设计了一款覆盖L 波段的宽带低温低噪声放大器(LNA),工作频率1 ~2GHz,相对带宽 达到66. 7%。在常温下放大器功率增益大于28dB,噪声温度小于39K;当环境温度制冷至11K 时,噪声温度为1. 9 ~3. 1K,输入输出端口的回波损耗S11 和S22 均优于-10dB,1dB 压缩点输出功率为9. 2dBm,功耗仅为54mW。     

Beam steering in high-power CW quantum-cascade lasers

We report the light-current (L-I), spectral, and far-field characteristics of quantum cascade lasers (QCLs) with seven different wavelengths in the /spl lambda/=4.3 to 6.3 /spl mu/m range. In continuous-wave (CW) mode, the narrow-stripe (/spl ap/13 /spl mu/m) epitaxial- side-up devices operated at temperatures up to 340 K, while at 295 K the CW output power was as high as 640 mW with a wallplug efficiency of 4.5%. All devices with /spl lambda//spl ges/4.7 /spl mu/m achieved room-temperature CW operation, and at T=200 K several produced powers exceeding 1 W with /spl ap/10% wallplug efficiency. The data indicated both spectral and spatial instabilities of the optical modes. For example, minor variations of the current often produced nonmonotonic hopping between spectra with envelopes as narrow as 5-10 nm or as broad as 200-250 nm. Bistable beam steering, by far-field angles of up to /spl plusmn/12/spl deg/ from the facet normal, also occurred, although even in extreme cases the beam quality never became worse than twice the diffraction limit. The observed steering is consistent with a theory for interference and beating between the two lowest order lateral modes. We also describe simulations of a wide-stripe photonic-crystal distributed-feedback QCL, which based on the current material quality is projected to emit multiple watts of CW power into a single-mode beam at T=200 K.     

Photopumped lasing at 1.25 /spl mu/m of GaInNAs-GaAs multiple-quantum-well vertical-cavity surface-emitting lasers

We report room-temperature (RT) continuous-wave (CW) photopumped operation of long-wavelength vertical-cavity surface-emitting lasers (VCSELs) employing a Ga/sub 0.7/In/sub 0.3/N/sub 0.007/As/sub 0.993/-GaAs multiple-quantum-well (MQW) active layer grown directly on a GaAs-AlAs distributed Bragg reflector (DBR). Evidence for laser oscillation includes spectral linewidth narrowing, clamping of spontaneous emission, and a distinct increase in slope efficiency at threshold. By taking advantage of lateral growth rate nonuniformity, we obtained laser emission over an extremely broad 110-nm wavelength range, from 1.146-1.256 /spl mu/m. Equivalent threshold current density over this range was estimated at 3.3-10 kA/cm/sup 2/.     

1.1-μm-Range High-Speed Tunnel Junction Vertical-Cavity Surface-Emitting Lasers

We have developed novel 1.1-mum-range buried type-II tunnel junction vertical-cavity surface-emitting lasers (VCSELs) with a dielectric mirror for high-speed optical interconnections. A relaxation oscillation frequency of 27 GHz was achieved. The maximum 3-dB bandwidth was over 24 GHz. Error-free 30-Gb/s operation using a 2⁷ -1-length pseudorandom bit sequence was demonstrated using directly modulated multimode VCSELs.     

Wide operating wavelength range and low threshold currentIn0.24Ga0.76As/GaAs vertical-cavitysurface-emitting lasers

Very low threshold current density operation of triple quantum well vertical-cavity surface-emitting lasers (VCSELs) is reported. The active wells are strained In_0.24Ga_0.76As in GaAs. Devices from the same wafer operate at room temperature over a wavelength range of 958-1042 nm, with a minimum threshold current density of 366 A-cm^-2 at 1018 nm. The dependence of threshold current on wavelength gives an insight into the optical gain spectrum of the quantum wells. It was shown that 50-μm-diameter devices operate CW without heatsinking     

Highly nondegenerate four-wave mixing among subpicosecond opticalpulses in a semiconductor optical amplifier

We have demonstrated, for the first time, the highly nondegenerate four-wave mixing (FWM) among subpicosecond optical pulses in a 1.3-μm multiple-quantum-well (MQW) semiconductor optical amplifier (SOA). We could directly measure the FWM signal in the output spectrum by current pulse pumping of the device. We achieved a high conversion efficiency of over 10% at a frequency conversion range of less than 1 THz. The limitation of conversion efficiency due to the gain saturation of the SOA was effectively overcome by using the short optical pulses     

In(Al)GaAs–AlGaAs Wafer Fused VCSELs Emitting at 2- μm Wavelength

We demonstrate 2-mum wavelength, wafer-fused In(Al)GaAs-InP-AlGaAs-GaAs vertical-cavity surface-emitting lasers (VCSELs) emitting single-mode power of 0.5 mW at room temperature with a threshold current of 4 mA and sidemode suppression ratio of over 30 dB. These devices can be continuously tuned with current by 5 nm without mode hopping, with a tuning rate of 0.31 nm/mA. These features demonstrate the potential of these long wavelength VCSELs for gas sensing and other optical spectroscopy applications.     

230 and 492 GHz low noise sis waveguide receivers employing tuned Nb/AlOx/Nb tunnel junctions

We report results on two full height waveguide receivers that cover the 200–290 GHz and 380–510 GHz atmospheric windows. The receivers are part of the facility instrumentation at the Caltech Submillimeter Observatory on Mauna Kea in Hawaii. We have measured receiver noise temperatures in the range of 20K–35K DSB in the 200–290 GHz band, and 65–90K DSB in the 390–510 GHz atmospheric band. In both instances low mixer noise temperatures and very high quantum efficiency have been achieved. Conversion gain (3 dB) is possible with the 230 GHz receiver, however lowest noise and most stable operation is achieved with unity conversion gain. A 40% operating bandwidth is achieved by using a RF compensated junction mounted in a two-tuner full height waveguide mixer block. The tuned Nb/AlO _x /Nb tunnel junctions incorporate an “end-loaded” tuning stub with two quarter-wave transformer sections to tune out the large junction capacitance. Both 230 and 492 GHz SIS junctions are 0.49µm² in size and have current densities of 8 and 10 kA/cm² respectively. Fourier Transform Spectrometer (FTS) measurements of the 230 and 492 GHz tuned junctions show good agreement with the measured heterodyne waveguide response.     

Microwave properties of low-loss polymers at cryogenic temperatures

Dielectric loss tangent and permittivity of polytetrafluoroethylene (Teflon), high-density (HD) polyethylene, and cross-linked polystyrene (Rexolite) were measured at temperature range from 28 to 84 K and frequency of approximately 18 GHz. The material properties were determined by measurements of the resonant frequency and the Q factor of a TE₀₁₁ mode cylindrical superconducting cavity containing a sample under test. It has been demonstrated that these materials exhibit very low losses at cryogenic temperatures (2×10^-6 for Teflon, 5×10^-5 for HD polyethylene and 1.1×10^-4 for Rexolite). Due to low losses, these materials can be useful in construction of various high-Q factor microwave devices for operation at cryogenic temperatures