A multi-hole vertical-cavity surface-emitting laser （VCSEL） operating in stable single mode with a low threshold current was produced by introducing multi-leaf scallop holes on the top distributed Bragg-refleetor of...A multi-hole vertical-cavity surface-emitting laser （VCSEL） operating in stable single mode with a low threshold current was produced by introducing multi-leaf scallop holes on the top distributed Bragg-refleetor of an oxidation- confined 850 nm VCSEL. The single-mode output power of 2.6 mW, threshold current of 0.6 mA, full width of half maximum lasing spectrum of less than 0.1 nm, side mode suppression ratio of 28.4 dB, and far-field divergence angle of about 10% are obtained. The effects of different hole depths on the optical characteristics are simulated and analysed, including far-field divergence, spectrum and lateral cavity mode. The single-mode performance of this multi-hole device is attributed to the large radiation loss from the inter hole spacing and the scattering loss at the bottom of the holes, particularly for higher order modes.展开更多
In this paper,the frequency-locking and threshold current-lowering effects of a quantum cascade laser are studied and achieved.Combined with cavity-enhanced absorption spectroscopy,the noninvasive detection of H_2 wit...In this paper,the frequency-locking and threshold current-lowering effects of a quantum cascade laser are studied and achieved.Combined with cavity-enhanced absorption spectroscopy,the noninvasive detection of H_2 with a prepared concentration of 500 ppm in multiple dissolved gases is performed and evaluated.The high frequency selectivity of 0.0051 cm^-1 at an acquisition time of 1 s allows the sensitive detection of the（1-0） S（l） band of H_2 with a high accuracy of（96.53±0.29）%and shows that the detection limit to an absorption line of 4712.9046 cm^-1 is approximately（17.26±0.63） ppm at an atmospheric pressure and a temperature of 20 ℃.展开更多
Threshold current characteristics of intracavity-contacted oxide-confinedvertical-cavity surface-emitting laser had been investigated in detail. Threshold currentcharacteristics not only were depended on the size of o...Threshold current characteristics of intracavity-contacted oxide-confinedvertical-cavity surface-emitting laser had been investigated in detail. Threshold currentcharacteristics not only were depended on the size of oxide-aperture, but also were also stronglyaffected by the mismatch of its lasing mode and gain peak. For the same degree detuning of the gainpeak and lasing mode at room temperature, the threshold current was approximately proportional tothe square of the oxide-aperture diameter of above 5 μm. For the same oxide-aperture device, thelarger the detuning degree of the lasing mode shifted to the shorter wavelength of the gain peak atroom temperature was, the lower the minimum threshold current was. The wavelengths of the lasingmode and gain peak were ± N X 10 nm detuning at 300 K, The temperature of the minimum thresholdcurrent was changed to be about ± N X 40 K(N real number). The calculated results were consistentwith the experimental ones.展开更多
We report on the room-temperature cascade laser （QCL） at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback （DFB） quantum optimization are used to decrease the thre...We report on the room-temperature cascade laser （QCL） at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback （DFB） quantum optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-μm-wide and 4- mm-long laser, high wall-plug efficiency of 6% is obtained at 20℃ from a single facet producing over I W of ew output power. The threshold current density of DFB QCL is as low as 1.13kA/cm^2 at 10℃ and 1.34kA/cm2 at 30℃ in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in tile working temperature range of 20-50℃.展开更多
The two-dimensional models for symmetrical double-material double-gate （DM-DG） strained Si （s-Si） metal-oxide semiconductor field effect transistors （MOSFETs） are presented. The surface potential and the surface...The two-dimensional models for symmetrical double-material double-gate （DM-DG） strained Si （s-Si） metal-oxide semiconductor field effect transistors （MOSFETs） are presented. The surface potential and the surface electric field ex- pressions have been obtained by solving Poisson＇s equation. The models of threshold voltage and subthreshold current are obtained based on the surface potential expression. The surface potential and the surface electric field are compared with those of single-material double-gate （SM-DG） MOSFETs. The effects of different device parameters on the threshold voltage and the subthreshold current are demonstrated. The analytical models give deep insight into the device parameters design. The analytical results obtained from the proposed models show good matching with the simulation results using DESSIS.展开更多
The inhomogeneous broadening parameter and the internal loss of green LDs are determined by experiments and theoretical fitting. It is found that the inhomogeneous broadening plays an important role on the threshold c...The inhomogeneous broadening parameter and the internal loss of green LDs are determined by experiments and theoretical fitting. It is found that the inhomogeneous broadening plays an important role on the threshold current density of green LDs. The green LD with large inhomogeneous broadening even cannot lase. Therefore, reducing inhomogeneous broadening is a key issue to improve the performance of green LDs.展开更多
The paper mainly deals with theoretical investigations of the effect of the thickness change of the wave- guide layers on the threshold current. It is analyzed according to the result of a numerical simulation that as...The paper mainly deals with theoretical investigations of the effect of the thickness change of the wave- guide layers on the threshold current. It is analyzed according to the result of a numerical simulation that asks how does the shift of the active region position affect the threshold current for a single quantum well （SQW） and double quantum well （DQW） laser diode （LD） with a relatively narrow waveguide. It is found that the variation trend of threshold current and optimum position of QW are different in SQW and DQW LD with 0.2 μm-thick waveguide, which may be due to the higher variation rate of optical loss in DQW LD with the shift of the active region. It is also found that in terms of either SQW or DQW LD, the variation tendency of the threshold current with a different loss coefficient of the p-cladding layer makes little difference for the relatively narrow waveguide LD. Moreover, the variation trend of the threshold current and the optimum position of QW is almost the same in SQW and DQW LD with 0.8 μm-thick waveguide, because the optical loss is small enough and the threshold current is dominated by the optical confinement factor （OCF） in QW.展开更多
Electroluminescence （EL） and temperature-dependent photolumineseenee measurements are performed to study the internal quantum efficiency droop phenomenon of blue laser diodes （LDs） before lasing. Based on the ABC ...Electroluminescence （EL） and temperature-dependent photolumineseenee measurements are performed to study the internal quantum efficiency droop phenomenon of blue laser diodes （LDs） before lasing. Based on the ABC mode, the EL result demonstrates that non-radiative recombination rates of LDs with threshold current densities of 4 and 6kA/cm2 are similar, while LD with threshold current density of 4kA/cm2 exhibits a smaller auger- like recombination rate compared with the one of 6kA/cm2. The internal quantum efficiency droop is more serious for LD with higher threshold current density. temperature-dependent photoluminescence is consistent The internal quantum efficiency value estimated from with EL measurements.展开更多
This paper proposes an equivalent circuit model to analyze the reason for the dispersion of sub-threshold current （also known as zero-current point dispersion） in organic thin-film transistors. Based on the level 61...This paper proposes an equivalent circuit model to analyze the reason for the dispersion of sub-threshold current （also known as zero-current point dispersion） in organic thin-film transistors. Based on the level 61 amorphous silicon thin-film transistor model in star-HSPICE, the results from our equivalent circuit model simulation reveal that zero-current point dispersion can be attributed to two factors： large contact resistance and small gate resistance. Furthermore, it is found that decreasing the contact resistance and increasing the gate resistance can efficiently reduce the dispersion. If the contact resistance can be controlled to 0 g2, all the zero-current points can gather together at the base point. A large gate resistance is good for constraining the dispersion of the zero-current points and gate leakage. The variances of the zero-current points are 0.0057 and nearly 0 when the gate resistances are 17 MΩ and 276 MΩ, respectively.展开更多
A generalized mathematical model of human body current threshold for perception was established and the current flowing through human body could be arbitrary cyclical waveforms.The relationship between human body curr...A generalized mathematical model of human body current threshold for perception was established and the current flowing through human body could be arbitrary cyclical waveforms.The relationship between human body current threshold for perception and current frequency, true root mean square(RMS) value and influence factor was described.A test system was established based on electroencephalogram(EEG) to study the relationship between human body current threshold for perception and current waveform, frequency ...展开更多
Objective： To quantitatively identify and grade trigeminal sensory functions after 3 major surgical procedures of trigeminal neuralgia using a newly developed quantitative sensory testing technique, current perceptio...Objective： To quantitatively identify and grade trigeminal sensory functions after 3 major surgical procedures of trigeminal neuralgia using a newly developed quantitative sensory testing technique, current perception threshold measurement （CPTM）. Methods： In the current study, there were 48 trigeminal neuralgia patients without history of prior surgical treatment. These patients received one of the following 3 surgical procedures, microvascular decompression （MVD）, peripheral nerve block with alcohol （PNB）, or percutaneous radiofrequency thermocoagulation （PRFT）. The quantitative sensory testing measurement, CPTM, and conventional qualitative sensory testing measurements were performed preoperatively and postoperatively to evaluate and grade the trigeminal sensory functions All 3 major cutaneous sensory fiber types, large myelinated fibers （A beta）, small myelinated fibers （A delta） and unmyelinated fibers（C） were allowed to quantitatively evaluate and grade by CPTM. The results of the measurements were statistically analyzed using a one-way analysis of variance （single factor）. Each subject was his/her own control for comparison of the preoperative to postoperative state on the asymptomatic and symptomatic sides. Subjects were tested 48 h preoperatively and 4 weeks postoperatively. Results： PNB with alcohol and PRFT caused significant sensory dysfunction postoperatively in every fiber type, indicating damage to all fibers. On the contrary, the sensory function in all 3 fiber types was unchanged after MVD management. Conclusion： Among the 3 major surgical procedures tested, only MVD preserves sensory function in trigeminal system. CPTM is of quantitative nature on the evaluation of sensory functions of nerve fibers展开更多
A strain-compensated InP-based quantum cascade laser（QCL） structure emitting at 4.6 μm is demonstrated,based on a two-phonon resonant design and grown by solid-source molecular beam epitaxy（MBE）.By optimizing the...A strain-compensated InP-based quantum cascade laser（QCL） structure emitting at 4.6 μm is demonstrated,based on a two-phonon resonant design and grown by solid-source molecular beam epitaxy（MBE）.By optimizing the growth parameters,a very high quality heterostructure with the lowest threshold current densities ever reported for QCLs was fabricated.Threshold current densities as low as 0.47 kA/cm^2 in pulsed operation and 0.56 kA/cm^2 in continuous-wave（cw） operation at 293 K were achieved for this state-of-the-art QCL.A minimum power consumption of 3.65 W was measured for the QCL,uncooled,with a high-reflectivity（HR） coating on its rear facet.展开更多
基金Project supported by the National High Technology Research and Development Program of China (Grant No. 2008AA03Z402)the National Natural Science Foundation of China (Grant No. 61076044)the Natural Science Foundation of Beijing,China(Grant Nos. 4092007 and 4102003)
文摘A multi-hole vertical-cavity surface-emitting laser （VCSEL） operating in stable single mode with a low threshold current was produced by introducing multi-leaf scallop holes on the top distributed Bragg-refleetor of an oxidation- confined 850 nm VCSEL. The single-mode output power of 2.6 mW, threshold current of 0.6 mA, full width of half maximum lasing spectrum of less than 0.1 nm, side mode suppression ratio of 28.4 dB, and far-field divergence angle of about 10% are obtained. The effects of different hole depths on the optical characteristics are simulated and analysed, including far-field divergence, spectrum and lateral cavity mode. The single-mode performance of this multi-hole device is attributed to the large radiation loss from the inter hole spacing and the scattering loss at the bottom of the holes, particularly for higher order modes.
基金supported by the Special Funds for the Development of National Major Scientific Instruments and Equipment,China(Grant No.2012YQ160007)the National Natural Science Foundation of China(Grant No.51277185)
文摘In this paper,the frequency-locking and threshold current-lowering effects of a quantum cascade laser are studied and achieved.Combined with cavity-enhanced absorption spectroscopy,the noninvasive detection of H_2 with a prepared concentration of 500 ppm in multiple dissolved gases is performed and evaluated.The high frequency selectivity of 0.0051 cm^-1 at an acquisition time of 1 s allows the sensitive detection of the（1-0） S（l） band of H_2 with a high accuracy of（96.53±0.29）%and shows that the detection limit to an absorption line of 4712.9046 cm^-1 is approximately（17.26±0.63） ppm at an atmospheric pressure and a temperature of 20 ℃.
基金National Natural Science Foundation of China ( 60276033 ) National High Technology Research and Development Program of china(2002AA312070)+1 种基金 National Key Basic Research Plan of china(G20000683-02) Beijing Natural Science Foundation of China
文摘Threshold current characteristics of intracavity-contacted oxide-confinedvertical-cavity surface-emitting laser had been investigated in detail. Threshold currentcharacteristics not only were depended on the size of oxide-aperture, but also were also stronglyaffected by the mismatch of its lasing mode and gain peak. For the same degree detuning of the gainpeak and lasing mode at room temperature, the threshold current was approximately proportional tothe square of the oxide-aperture diameter of above 5 μm. For the same oxide-aperture device, thelarger the detuning degree of the lasing mode shifted to the shorter wavelength of the gain peak atroom temperature was, the lower the minimum threshold current was. The wavelengths of the lasingmode and gain peak were ± N X 10 nm detuning at 300 K, The temperature of the minimum thresholdcurrent was changed to be about ± N X 40 K(N real number). The calculated results were consistentwith the experimental ones.
基金Supported by the National Basic Research Program of China under Grant Nos 2013CB632801 and 2013CB632803the National Natural Science Foundation of China under Grant Nos 61435014,61306058 and 61274094the Beijing Natural Science Foundation under Grant No 4144086
文摘We report on the room-temperature cascade laser （QCL） at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback （DFB） quantum optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-μm-wide and 4- mm-long laser, high wall-plug efficiency of 6% is obtained at 20℃ from a single facet producing over I W of ew output power. The threshold current density of DFB QCL is as low as 1.13kA/cm^2 at 10℃ and 1.34kA/cm2 at 30℃ in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in tile working temperature range of 20-50℃.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61376099,11235008,and 61205003)
文摘The two-dimensional models for symmetrical double-material double-gate （DM-DG） strained Si （s-Si） metal-oxide semiconductor field effect transistors （MOSFETs） are presented. The surface potential and the surface electric field ex- pressions have been obtained by solving Poisson＇s equation. The models of threshold voltage and subthreshold current are obtained based on the surface potential expression. The surface potential and the surface electric field are compared with those of single-material double-gate （SM-DG） MOSFETs. The effects of different device parameters on the threshold voltage and the subthreshold current are demonstrated. The analytical models give deep insight into the device parameters design. The analytical results obtained from the proposed models show good matching with the simulation results using DESSIS.
基金supported by the National Key Research and Development Program of China(Grant Nos.2017YFB0405000,2016YFB0401803)the National Natural Science Foundation of China(Grant Nos.61834008,61574160,and 61704184)support of the Chinese Academy of Science Visiting Professorship for Senior International Scientists (Grant No.2013T2J0048)
文摘The inhomogeneous broadening parameter and the internal loss of green LDs are determined by experiments and theoretical fitting. It is found that the inhomogeneous broadening plays an important role on the threshold current density of green LDs. The green LD with large inhomogeneous broadening even cannot lase. Therefore, reducing inhomogeneous broadening is a key issue to improve the performance of green LDs.
文摘The paper mainly deals with theoretical investigations of the effect of the thickness change of the wave- guide layers on the threshold current. It is analyzed according to the result of a numerical simulation that asks how does the shift of the active region position affect the threshold current for a single quantum well （SQW） and double quantum well （DQW） laser diode （LD） with a relatively narrow waveguide. It is found that the variation trend of threshold current and optimum position of QW are different in SQW and DQW LD with 0.2 μm-thick waveguide, which may be due to the higher variation rate of optical loss in DQW LD with the shift of the active region. It is also found that in terms of either SQW or DQW LD, the variation tendency of the threshold current with a different loss coefficient of the p-cladding layer makes little difference for the relatively narrow waveguide LD. Moreover, the variation trend of the threshold current and the optimum position of QW is almost the same in SQW and DQW LD with 0.8 μm-thick waveguide, because the optical loss is small enough and the threshold current is dominated by the optical confinement factor （OCF） in QW.
基金Supported by the National Key Research and Development Program of China under Grant Nos 2016YFB0401803 and 2016YFB0402002the National Natural Science Foundation of China under Grant Nos 61574160 and 61334005+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No XDA09020401the Visiting Professorship for Senior International Scientists of the Chinese Academy of Sciences under Grant No 2013T2J0048
文摘Electroluminescence （EL） and temperature-dependent photolumineseenee measurements are performed to study the internal quantum efficiency droop phenomenon of blue laser diodes （LDs） before lasing. Based on the ABC mode, the EL result demonstrates that non-radiative recombination rates of LDs with threshold current densities of 4 and 6kA/cm2 are similar, while LD with threshold current density of 4kA/cm2 exhibits a smaller auger- like recombination rate compared with the one of 6kA/cm2. The internal quantum efficiency droop is more serious for LD with higher threshold current density. temperature-dependent photoluminescence is consistent The internal quantum efficiency value estimated from with EL measurements.
文摘This paper proposes an equivalent circuit model to analyze the reason for the dispersion of sub-threshold current （also known as zero-current point dispersion） in organic thin-film transistors. Based on the level 61 amorphous silicon thin-film transistor model in star-HSPICE, the results from our equivalent circuit model simulation reveal that zero-current point dispersion can be attributed to two factors： large contact resistance and small gate resistance. Furthermore, it is found that decreasing the contact resistance and increasing the gate resistance can efficiently reduce the dispersion. If the contact resistance can be controlled to 0 g2, all the zero-current points can gather together at the base point. A large gate resistance is good for constraining the dispersion of the zero-current points and gate leakage. The variances of the zero-current points are 0.0057 and nearly 0 when the gate resistances are 17 MΩ and 276 MΩ, respectively.
基金Supported by the Ministry of Science and Technology of China (No. NCSTE-2006-JKZX-167)Beijing Key Laboratory (Measurement and Control of Electro-mechanical Systems) (No. 82063005)
文摘A generalized mathematical model of human body current threshold for perception was established and the current flowing through human body could be arbitrary cyclical waveforms.The relationship between human body current threshold for perception and current frequency, true root mean square(RMS) value and influence factor was described.A test system was established based on electroencephalogram(EEG) to study the relationship between human body current threshold for perception and current waveform, frequency ...
文摘Objective： To quantitatively identify and grade trigeminal sensory functions after 3 major surgical procedures of trigeminal neuralgia using a newly developed quantitative sensory testing technique, current perception threshold measurement （CPTM）. Methods： In the current study, there were 48 trigeminal neuralgia patients without history of prior surgical treatment. These patients received one of the following 3 surgical procedures, microvascular decompression （MVD）, peripheral nerve block with alcohol （PNB）, or percutaneous radiofrequency thermocoagulation （PRFT）. The quantitative sensory testing measurement, CPTM, and conventional qualitative sensory testing measurements were performed preoperatively and postoperatively to evaluate and grade the trigeminal sensory functions All 3 major cutaneous sensory fiber types, large myelinated fibers （A beta）, small myelinated fibers （A delta） and unmyelinated fibers（C） were allowed to quantitatively evaluate and grade by CPTM. The results of the measurements were statistically analyzed using a one-way analysis of variance （single factor）. Each subject was his/her own control for comparison of the preoperative to postoperative state on the asymptomatic and symptomatic sides. Subjects were tested 48 h preoperatively and 4 weeks postoperatively. Results： PNB with alcohol and PRFT caused significant sensory dysfunction postoperatively in every fiber type, indicating damage to all fibers. On the contrary, the sensory function in all 3 fiber types was unchanged after MVD management. Conclusion： Among the 3 major surgical procedures tested, only MVD preserves sensory function in trigeminal system. CPTM is of quantitative nature on the evaluation of sensory functions of nerve fibers
基金supported by the National Basic Research Program of China(Grant Nos.2013CB632801 and 2013CB632803)the National Natural Science Foundation of China(Grant Nos.61306058,61274094,and 61435014)the Beijing Natural Science Foundation(Grant No.4144086)
文摘A strain-compensated InP-based quantum cascade laser（QCL） structure emitting at 4.6 μm is demonstrated,based on a two-phonon resonant design and grown by solid-source molecular beam epitaxy（MBE）.By optimizing the growth parameters,a very high quality heterostructure with the lowest threshold current densities ever reported for QCLs was fabricated.Threshold current densities as low as 0.47 kA/cm^2 in pulsed operation and 0.56 kA/cm^2 in continuous-wave（cw） operation at 293 K were achieved for this state-of-the-art QCL.A minimum power consumption of 3.65 W was measured for the QCL,uncooled,with a high-reflectivity（HR） coating on its rear facet.
