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
Previous studies have shown some correlations between the optical properties of objects and their surface patterns. We fabricate tens of micrometer period gratings by femtosecond laser direct writing technology on pol...Previous studies have shown some correlations between the optical properties of objects and their surface patterns. We fabricate tens of micrometer period gratings by femtosecond laser direct writing technology on polished nickel targets and measure their thermal radiation spectra at a temperature of 623 K by Fourier transform infrared （FTIR） spectrometry. The results show an obvious major enhanced peak in which the wavelength is slightly larger than the grating period. Surface plasmon resonance （SPR） and Kircbhoff＇s law of thermal radiation are applied to give this phenomenon a preliminary explanation. In addition, we utilized rigorous coupled wave analysis （RCWA） to simulate the absorption spectrum of the grating surface. The experiment results show good agreement with the simulation results.展开更多
A new type of 785 nm semiconductor laser device has been proposed.The thin cladding and mode expansion layer structure incorporated into the epitaxy on the p-side significantly impacts the regulation of grating etchin...A new type of 785 nm semiconductor laser device has been proposed.The thin cladding and mode expansion layer structure incorporated into the epitaxy on the p-side significantly impacts the regulation of grating etching depth.Thinning of the p-side waveguide layer makes the light field bias to the n-side cladding layer.By coordinating the confinement effect of the cladding layer,the light confinement factor on the p-side is regulated.On the other hand,the introduction of a mode expansion layer facilitates the expansion of the mode profile on the p side cladding layer.Both these factors contribute positively to reducing the grating etching depth.Compared to the reported epitaxial structures of symmetric waveguides,the new structure significantly reduces the etching depth of the grating while ensuring adequate reflection intensity and maintaining resonance.Moreover,to improve the output performance of the device,the new epitaxial structure has been optimized.Based on the traditional epitaxial structure,an energy release layer and an electron blocking layer are added to improve the electronic recombination efficiency.This improved structure has an output performance comparable to that of a symmetric waveguide,despite being able to have a smaller gain area.展开更多
A grating surface can drive the liquid crystal molecules to orientate along the direction parallel or vertical to the projected plane of the grating surface. The nematic liquid crystal （NLC） cell manufactured with t...A grating surface can drive the liquid crystal molecules to orientate along the direction parallel or vertical to the projected plane of the grating surface. The nematic liquid crystal （NLC） cell manufactured with two pre-treated grating surface substrates may realize the vertical display, parallel display and twist display. In this paper, the threshold property of this NLC cell is investigated systematically. With the Frank elastic theory and the equivalent anchoring energy formula of grating surface substrate, the analytic expressions of the threshold voltage related to three displays are obtained, which are dependent on their geometrical parameters such as amplitude ~ and pitch A of the grating surface substrate. For a certain anchoring strength, the threshold voltage increases or decreases with the increase of the value δ/λ of the different displays.展开更多
High Q reflection filter using a gradient-index(GI) membrane with a grating surface is proposed. The thickness of GI membrane is very small comparing with the traditional multilayer reflection filter or the GI reflect...High Q reflection filter using a gradient-index(GI) membrane with a grating surface is proposed. The thickness of GI membrane is very small comparing with the traditional multilayer reflection filter or the GI reflection filter, and the GI membrane can also break the restriction of the resonant excitation condition of the conventional guided-mode resonance(GMR) filter. High Q filtering features can be maintained even on the high-index substrate. The grating thickness of the GI membrane filter can be used to select the resonance wavelength with different quality factors(QFs), the reflection peak is blue-shifted, and the QF is decreased from 554.4 to 207.8 as the grating thickness is increased from 50 nm to 150 nm. The gradient coefficient of the GI membrane filter can be used to tailor the number of the reflection channels. The resonant excitations of high order waveguide modes confined in the GI membrane are responsible for the high Q filtering properties with multiple channels.展开更多
A theoretical method is presented,which analyzes properties of surface acoustic waves propagating on metallic gratings with finite thickness by combining finite element method with variational principle on surface aco...A theoretical method is presented,which analyzes properties of surface acoustic waves propagating on metallic gratings with finite thickness by combining finite element method with variational principle on surface acoustic waves propagating on periodic metal gratings. Based on D.P.Chen and Haus theory,a finite element method is used to investigate the effects of metallic gratings upon the propagation of surface acoustic waves.The coupling-of-modes parameters contributed by mechanical loading are expressed by the matrix derived from the finite element method.Consequently D.P.Chen and Haus theory can also be applied to analyze the properties of surface acoustic waves propagating on metallic gratings with finite thickness and arbitrary shape.Finally,the characteristics of surface acoustic waves propagating under gold and aluminum or silver gratings on a few piezoelectric crystals are studied.Numerical results of the coupling-of-modes parameters of the surface acoustic waves are obtained.展开更多
We report a novel lateral cavity surface emitting laser based on sub-wavelength high-index-contrast grating with in-plane resonance and surface-normal emission. The device is fabricated on a simple commercial wafer wi...We report a novel lateral cavity surface emitting laser based on sub-wavelength high-index-contrast grating with in-plane resonance and surface-normal emission. The device is fabricated on a simple commercial wafer without the distributed Bragg reflector and it needs no wafer bonding. It exhibits a side mode suppression ratio of 23.0 d B and a high output power of 5.32 m W at 1552.44 nm. The specific single mode lasing agrees well with the band edge mode calculation of the grating. In 3D simulation, we observe obvious light output from the grating.展开更多
An analytical expression for the focal intensity of a laser pulse was obtained for an asymmetric out-of-plane compressor with gratings of arbitrary surface shape. The focal intensity is most strongly affected by the l...An analytical expression for the focal intensity of a laser pulse was obtained for an asymmetric out-of-plane compressor with gratings of arbitrary surface shape. The focal intensity is most strongly affected by the linear angular chirp caused by the spatial shift of different frequencies on the second and third gratings. The chirp can be eliminated by simply rotating the fourth grating by an optimal angle, which significantly reduces the requirements for the grating quality. It is shown that the decrease in the focal intensity depends on the product of the grating surface root mean square and pulse spectrum bandwidth. With low-quality gratings, spectrum narrowing would not reduce focal intensity;contrariwise, it may even slightly increase it.展开更多
Augmented reality(AR)displays,as the next generation platform for spatial computing and digital twins,enable users to view digital images superimposed on real-world environment,fostering a deeper level of human-digita...Augmented reality(AR)displays,as the next generation platform for spatial computing and digital twins,enable users to view digital images superimposed on real-world environment,fostering a deeper level of human-digital interactions.However,as a critical element in an AR system,optical combiners face unprecedented challenges to match the exceptional performance requirements of human vision system while keeping the headset ultracompact and lightweight.After decades of extensive device and material research efforts,and heavy investment in manufacturing technologies,several promising waveguide combiners have been developed.In this review paper,we focus on the perspectives and challenges of optical waveguide combiners for AR displays.We will begin by introducing the basic device structures and operation principles of different AR architectures,and then delve into different waveguide combiners,including geometric and diffractive waveguide combiners.Some commonly used in-couplers and out-couplers,such as prisms,mirrors,surface relief gratings,volume holographic gratings,polarization volume gratings,and metasurface-based couplers,will be discussed,and their properties analyzed in detail.Additionally,we will explore recent advances in waveguide combiner design and modeling,such as exit pupil expansion,wide field of view,geometric architectures of waveguide couplers,full-color propagation,and brightness and color uniformity optimization.Finally,we will discuss the bottlenecks and future development trends in waveguide combiner technologies.The objective of this review is to provide a comprehensive overview of the current state of waveguide combiner technologies,analyze their pros and cons,and then present the future challenges of AR displays.展开更多
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supported by the National Natural Science Foundation of China(Grant No.51275012)
文摘Previous studies have shown some correlations between the optical properties of objects and their surface patterns. We fabricate tens of micrometer period gratings by femtosecond laser direct writing technology on polished nickel targets and measure their thermal radiation spectra at a temperature of 623 K by Fourier transform infrared （FTIR） spectrometry. The results show an obvious major enhanced peak in which the wavelength is slightly larger than the grating period. Surface plasmon resonance （SPR） and Kircbhoff＇s law of thermal radiation are applied to give this phenomenon a preliminary explanation. In addition, we utilized rigorous coupled wave analysis （RCWA） to simulate the absorption spectrum of the grating surface. The experiment results show good agreement with the simulation results.
文摘A new type of 785 nm semiconductor laser device has been proposed.The thin cladding and mode expansion layer structure incorporated into the epitaxy on the p-side significantly impacts the regulation of grating etching depth.Thinning of the p-side waveguide layer makes the light field bias to the n-side cladding layer.By coordinating the confinement effect of the cladding layer,the light confinement factor on the p-side is regulated.On the other hand,the introduction of a mode expansion layer facilitates the expansion of the mode profile on the p side cladding layer.Both these factors contribute positively to reducing the grating etching depth.Compared to the reported epitaxial structures of symmetric waveguides,the new structure significantly reduces the etching depth of the grating while ensuring adequate reflection intensity and maintaining resonance.Moreover,to improve the output performance of the device,the new epitaxial structure has been optimized.Based on the traditional epitaxial structure,an energy release layer and an electron blocking layer are added to improve the electronic recombination efficiency.This improved structure has an output performance comparable to that of a symmetric waveguide,despite being able to have a smaller gain area.
基金Project supported by the Key Subject Construction Project of Hebei Province University of Chinathe National Natural Science Foundation of China (Grant Nos 10704022 and 60736042)
文摘A grating surface can drive the liquid crystal molecules to orientate along the direction parallel or vertical to the projected plane of the grating surface. The nematic liquid crystal （NLC） cell manufactured with two pre-treated grating surface substrates may realize the vertical display, parallel display and twist display. In this paper, the threshold property of this NLC cell is investigated systematically. With the Frank elastic theory and the equivalent anchoring energy formula of grating surface substrate, the analytic expressions of the threshold voltage related to three displays are obtained, which are dependent on their geometrical parameters such as amplitude ~ and pitch A of the grating surface substrate. For a certain anchoring strength, the threshold voltage increases or decreases with the increase of the value δ/λ of the different displays.
基金supported by the National Natural Science Foundation of China(No.11404143)the Fundamental Research Funds for the Central Universities(No.JUSRP115A15)the Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology(No.BM2014402)
文摘High Q reflection filter using a gradient-index(GI) membrane with a grating surface is proposed. The thickness of GI membrane is very small comparing with the traditional multilayer reflection filter or the GI reflection filter, and the GI membrane can also break the restriction of the resonant excitation condition of the conventional guided-mode resonance(GMR) filter. High Q filtering features can be maintained even on the high-index substrate. The grating thickness of the GI membrane filter can be used to select the resonance wavelength with different quality factors(QFs), the reflection peak is blue-shifted, and the QF is decreased from 554.4 to 207.8 as the grating thickness is increased from 50 nm to 150 nm. The gradient coefficient of the GI membrane filter can be used to tailor the number of the reflection channels. The resonant excitations of high order waveguide modes confined in the GI membrane are responsible for the high Q filtering properties with multiple channels.
基金supported by the National Nature Science Foundation of China(10974171)Zhejiang Province Nature Science Foundation(LY12A04003)
文摘A theoretical method is presented,which analyzes properties of surface acoustic waves propagating on metallic gratings with finite thickness by combining finite element method with variational principle on surface acoustic waves propagating on periodic metal gratings. Based on D.P.Chen and Haus theory,a finite element method is used to investigate the effects of metallic gratings upon the propagation of surface acoustic waves.The coupling-of-modes parameters contributed by mechanical loading are expressed by the matrix derived from the finite element method.Consequently D.P.Chen and Haus theory can also be applied to analyze the properties of surface acoustic waves propagating on metallic gratings with finite thickness and arbitrary shape.Finally,the characteristics of surface acoustic waves propagating under gold and aluminum or silver gratings on a few piezoelectric crystals are studied.Numerical results of the coupling-of-modes parameters of the surface acoustic waves are obtained.
基金Project supported by the Chinese National Key Basic Research Special Fund/CNKBRSF(Nos.2012CB933501,2011CB922002)the National Natural Science Foundation of China(Nos.61025025,61137003,61234004,61021003)the National High Technology Research and Development Program of China(No.2012AA012202)
文摘We report a novel lateral cavity surface emitting laser based on sub-wavelength high-index-contrast grating with in-plane resonance and surface-normal emission. The device is fabricated on a simple commercial wafer without the distributed Bragg reflector and it needs no wafer bonding. It exhibits a side mode suppression ratio of 23.0 d B and a high output power of 5.32 m W at 1552.44 nm. The specific single mode lasing agrees well with the band edge mode calculation of the grating. In 3D simulation, we observe obvious light output from the grating.
基金supported by the Ministry of Science and Higher Education of the Russian Federation(075-15-2022-316,Center of Excellence‘Center of Photonics’)
文摘An analytical expression for the focal intensity of a laser pulse was obtained for an asymmetric out-of-plane compressor with gratings of arbitrary surface shape. The focal intensity is most strongly affected by the linear angular chirp caused by the spatial shift of different frequencies on the second and third gratings. The chirp can be eliminated by simply rotating the fourth grating by an optimal angle, which significantly reduces the requirements for the grating quality. It is shown that the decrease in the focal intensity depends on the product of the grating surface root mean square and pulse spectrum bandwidth. With low-quality gratings, spectrum narrowing would not reduce focal intensity;contrariwise, it may even slightly increase it.
文摘Augmented reality(AR)displays,as the next generation platform for spatial computing and digital twins,enable users to view digital images superimposed on real-world environment,fostering a deeper level of human-digital interactions.However,as a critical element in an AR system,optical combiners face unprecedented challenges to match the exceptional performance requirements of human vision system while keeping the headset ultracompact and lightweight.After decades of extensive device and material research efforts,and heavy investment in manufacturing technologies,several promising waveguide combiners have been developed.In this review paper,we focus on the perspectives and challenges of optical waveguide combiners for AR displays.We will begin by introducing the basic device structures and operation principles of different AR architectures,and then delve into different waveguide combiners,including geometric and diffractive waveguide combiners.Some commonly used in-couplers and out-couplers,such as prisms,mirrors,surface relief gratings,volume holographic gratings,polarization volume gratings,and metasurface-based couplers,will be discussed,and their properties analyzed in detail.Additionally,we will explore recent advances in waveguide combiner design and modeling,such as exit pupil expansion,wide field of view,geometric architectures of waveguide couplers,full-color propagation,and brightness and color uniformity optimization.Finally,we will discuss the bottlenecks and future development trends in waveguide combiner technologies.The objective of this review is to provide a comprehensive overview of the current state of waveguide combiner technologies,analyze their pros and cons,and then present the future challenges of AR displays.
