A broad-band waveguide grating coupler with a subwavelength grating mirror

A new diffractive device for light coupling between a planar optical waveguide and free space is proposed. The device utilizes a second-order waveguide grating to diffract the fundamental waveguide mode into two free propagating beams and a subwavelength grating (SWG) mirror to combine the two free propagating beams into a single beam. The finite-difference time-domain (FDTD) simulations show that the SWG mirror improves the coupling efficiency of the waveguide fundamental mode into the single out-coupled beam from about 30% to 92%. A high efficiency (>90%) is predicted for a broad wavelength range of 1520-1580nm. The proposed device is compact (/spl sim/80 /spl mu/m in length) and it eliminates the need for blazing the waveguide grating.     

Fabrication of biomimic GaAs subwavelength grating structures for broadband and angular-independent antireflection

We combine interferometric lithography and inductively coupled plasma etching to fabricate GaAs subwavelength grating (SWG) which mimics the moth eye structures. Through the modification of morphology parameters, including profile, height and packing fraction, tapered, high-aspect-ratio and closely-packed GaAs SWGs are obtained. The measurement of spectral reflectance of the fabricated SWGs shows that reflection has been dramatically reduced compared to the polished GaAs surface. Particularly, the optimized SWG structures exhibit an average reflection below 5% in the wavelengths ranging from 350 to 900 nm. Furthermore, the angular-independent property is demonstrated by measuring the reflectance versus varying angles of incidence at 532 and 632.8 nm wavelengths.     

LiNbO/sub 3/ waveguide SHG device with ferroelectric-domain-inverted grating formed by electron-beam scanning

A ferroelectric-domain-inverted grating was fabricated by electron beam scanning in LiNbO/sub 3/. A waveguide second harmonic generation (SHG) device with the grating was fabricated and demonstrated for the first time. The experiments were performed using a CW-Nd:YAG laser, and normalised SHG conversion efficiency of 50%/W was obtained.<>     

Monolithic integration of wavelength-scale diffractive structures on red vertical-cavity lasers by focused ion beam etching

We report the fabrication and characterization of wavelength-scale diffractive optical elements etched directly on the surface of red (660 nm) vertical-cavity surface-emitting lasers. The structures were fabricated by focused ion beam etching. Linear and two-dimensional (2-D) grating configurations were investigated. Each showed excellent suppression of the zeroth-order diffracted beam. Compared to the power from an unetched laser, /spl sim/22% of the emission was coupled into the first order for linear gratings and 12% for the 2-D structures. Polarization was independent of grating orientation for grating pitches as small as 1/spl lambda/. Threshold current increases of 35%-40% were measured.     

Broadly tunable external cavity laser diodes with staggered thickness multiple quantum wells

Widely tunable low-threshold current laser diodes fabricated from an engineered multiple-quantum-well (MQW) gain structure consisting of three compressively strained In/sub 0.2/Ga/sub 0.8/As wells of different thicknesses are reported. Using a grating in an external cavity, a continuous-wave tuning range of 70 nm (911-981 nm) is measured for a 155-/spl mu/m semiconductor cavity length device at a current of 32 mA. This is the lowest reported bias current for a semiconductor laser with this broad a tuning range. A maximum continuous wave tuning of 80 nm (901-981 nm) has been measured at a bias current of 95 mA. At long wavelengths, a suppression of amplified spontaneous emission and preferential population of the lowest energy well were observed.     

Broad-band mirror (1.12-1.62 /spl mu/m) using a subwavelength grating

We report the first experimental demonstration of a novel single-layer subwavelength grating (SWG) that has >500-nm-wide reflection spectrum from 1.12-1.62 /spl mu/m and very high reflectivity (>98.5%). This SWG is scalable for different wavelengths by simply changing the grating dimensions, which, thus, facilitates monolithic integration of devices over a wide range of wavelengths.     

纳米压印制作半导体激光器的分布反馈光栅

分布反馈(DFB)光栅的制作是半导体激光器芯片的关键工艺,通过纳米压印技术在InP基片表面涂覆的光刻胶上压印出DFB光栅图形,并分别通过湿法腐蚀和干法刻蚀技术将光栅图形转移到InP基片上。所制作的DFB光栅周期为240nm(对应于1 550nm波长的DFB激光器),光栅中间具有λ/4相移结构。采用纳米压印技术制作的DFB光栅相对于通常双光束干涉法制作的光栅具有更好的均匀性以及更低的线条粗糙度,而且解决了双光束干涉法无法制作非均匀光栅的技术难题。相对于电子束直写光刻法,采用纳米压印技术制作DFB光栅具有快速与低成本的优势。采用纳米压印技术在InP基片上成功制作具有相移结构的DFB光栅,为进一步进行低成本高性能的半导体激光器芯片的制作奠定了良好基础。     

Fabrication of Germanosilicate glass optical fibers containing Tm/sup 2+/ ions and their nonlinear optical properties

Germanosilicate glass optical fibers incorporated with the Tm/sup 2+/ ions were fabricated to enhance optical nonlinearity by providing a strong reduction environment based on the solution doping technique in the modified chemical vapor deposition (MCVD) process. The incorporation of the Tm/sup 2+/ ions into the fiber core was identified by the electron paramagnetic resonance (EPR) spectrum in the fiber preform, and the absorption and emission properties between 350 and 1600 nm of the Tm/sup 2+/ ions in optical fibers and the fiber preform. A strong broad absorption band due to the Tm/sup 2+/ ions appeared from 350 to /spl sim/900 nm, and a broad emission from /spl sim/600 to /spl sim/1050 nm and the other emission from /spl sim/1050 to /spl sim/1300 nm, which were not shown in the Tm/sup 3+/ ions, were found upon Ar-ion laser pumping at 515 nm. Both absorption and emission results confirm that the Tm/sup 2+/ ions in the germanosilicate glass have the 4f-5d energy band from 350 to /spl sim/900 nm and the 4f-4f energy level at /spl sim/1115 nm. Also, the resonant nonlinearity at /spl sim/1310 and /spl sim/1530 nm due to the Tm/sup 2+/ ions in the fiber was measured upon the 515 nm optical pumping by using a long-period fiber grating (LPG) pair method. The nonlinear refractive index n/sub 2/ at /spl sim/1310 and /spl sim/1530 nm was found to be /spl sim/4/spl times/10/sup -15/ m/sup 2//W, where 70% and 30% of the n/sub 2/ are attributed to the nonradiative transitions and the radiative transitions, respectively.     

Freestanding GaN Resonant Gratings at Telecommunication Range

We theoretically and experimentally demonstrate a freestanding gallium nitride (GaN) resonant grating at telecommunication range. The optical responses of the freestanding GaN resonant gratings are analyzed by the rigorous coupled-wave analysis method. The freestanding GaN resonant gratings are validated on 850-nm freestanding membrane by a combination of electron beam lithography, fast atom beam, etching, and deep reactive ion etching. The polarization properties of such freestanding GaN resonant gratings are demonstrated in reflectance measurements, and the experimental results correspond well to the theoretical model. The strong resonant peaks show a clear dependence on the duty ratio under transverse magnetic polarization, and a promising resonant peak of the fabricated freestanding GaN resonant grating, in which the grating period $P$ is 1500 nm, the grating height $h$ is 230 nm, and the grating width is 280 nm, is observed at 1516.4 nm with a full-width at half-maximum of 4 nm.      

12W high-brightness single-frequency DBR tapered diode laser

A distributed Bragg reflector (DBR) tapered diode laser with a record optical output power of 12 W and a conversion efficiency of about 44% is presented. The device has a sixth-order surface grating and shows single longitudinal mode emission at 979 nm as well as a nearly diffraction limited beam. At 11.4 W the laser has a lateral beam propagation factor of M ² _1/ e ²=1.1 with 72% of the power in the central lobe.     

Design and fabrication of ultra-small overlapped AWG demultiplexer based on /spl alpha/-Si nanowire waveguides

A novel layout for an ultra-compact arrayed-waveguide grating (AWG) demultiplexer is presented. The present layout has two overlapped free propagation regions, and is more compact than a conventional layout. Using /spl alpha/Si-on-SiO/sub 2/ nanowire waveguides, an ultra-small 4/spl times/4 AWG (about 40/spl times/50 /spl mu/m/sup 2/) with channel spacing of 11 nm is fabricated and characterised.     

Investigation of high-efficiency surface-emitting lasers withblazed grating outcouplers

Grating outcouplers for use in grating coupled surface emitting semiconductor lasers were investigated. For this purpose, horizontal cavity InGaAs-AlGaAs laser oscillators, each integrated with one detuned grating outcoupler, were fabricated using electron beam lithography and chemically assisted ion beam etching. Outcouplers with gratings of both rectangular and blazed profile as well as of different toothwidth-to-period ratios were fabricated and evaluated. Superior differential quantum and surface emission efficiencies of 56% and 84%, respectively, were measured for lasers with optimized blazed outcouplers. This shows that efficiencies comparable to those of conventional edge emitting lasers can be achieved. The measured surface emission efficiencies were also compared with predictions from a theoretical grating analysis     

Complex-coupled quantum cascade distributed-feedback laser

Quantum-cascade distributed-feedback lasers (QCDFB) with a grating close to the active region are reported. Feedback is provided by the grating in a refractive index-dominated coupling scheme. Reliable single-mode emission at /spl lambda//sub cm//spl ap/5.4 /spl mu/m with a side-mode suppression ratio (SMSR) /spl ap/30 dB is observed. The laser is continuously tunable over 40 nm with a coefficient of /spl Delta//spl lambda///spl Delta/T/spl ap/0.37 nm/K in the temperature range from 200 K to 300 K. Comparison with Fabry-Perot QC lasers shows an overall improved performance of QC-DFB lasers.     

离子束刻蚀位相型Ronchi光栅研究

本文报道了采用紫外光刻和离子束刻蚀方法制作位相型Ｒｏｎｃｈｉ光栅的工艺技术，并对其衍射特性进行了讨论，同时给出实验结果。     

离子束刻蚀正交位相型Ronchi光栅研究

本文报道了采用紫外光刻和离子束刻蚀方法制作正交位相互Ｒｏｎｃｈｉ的工艺技术,并讨伐春衍射效率,给出公式及实验结果。     

Polarization Control in Buried Tunnel Junction VCSELs Using a Birefringent Semiconductor/Dielectric Subwavelength Grating

We present long-wavelength InGaAlAs-InP vertical-cavity surface-emitting lasers (VCSELs) with a buried tunnel junction (BTJ) and a well-defined polarization accomplished by a semiconductor/dielectric subwavelength grating (SWG). The grating is incorporated in the inner VCSEL cavity and exhibits an effective birefringence for polarizations parallel and perpendicular to the grating grooves. Theoretical modeling leads to distinct design rules for VCSELs with grating structure that deviate from the conventional design without grating. Due to the large polarization-mode separation, lasing activity is enabled only for one polarization mode. BTJ-VCSELs with properly chosen SWG parameters show predictable and full polarization stability. In addition, the relevant device parameters such as threshold current are comparable to conventional BTJ-VCSELs.     

Rhombus-like stripe BA InGaAs-AlGaAs-GaAs lasers

A 1.5-W continuous-wave power output in a beam pattern of 3/spl deg/ is obtained from a new designed rhombus-like stripe strained quantum-well diode laser (/spl lambda/=980 nm) with a 150-/spl mu/m-wide emission aperture grown by molecular beam epitaxy. The /spl eta//sub d/ is as high as 78%, and the maximum output power by the new stripe laser is 5.0 W for antireflection/high-reflection coated devices.     

Facet and grating reflectivity effects in wavelength stabilised uncooled pump lasers

The performance of an uncooled 980 nm fibre Bragg grating stabilised pump laser in miniature dual-in-line package as a function of laser front facet reflectivity (R/sub f/) and grating reflectivity (R/sub g/) is reported. The quantitative analysis on workable bounds for R/sub f/ and R/sub g/ with multiple devices is presented.     

Spectral Properties of High-Power Distributed Bragg Reflector Lasers

In this paper, spectral data of distributed Bragg reflector lasers emitting around 974 nm and 1084 nm are presented. The devices are fabricated by a single-growth molecular beam epitaxy step, and the gratings are defined by holographic interferometry. Spectral dependencies on the grating and gain section lengths are systematically investigated in the so-called cleaved-back experiments. Experimental data for the side-mode suppression ratio, mode spacing, and group refractive index are given for devices emitting around 974 nm. In addition, the coupling efficiency between the grating and gain section is derived experimentally for devices emitting around 1084 nm.      

GaAs/AlGaAs grating surface-emitting diode lasers on Si substrates

A monolithic grating surface-emitting, GaAs/AlGaAs, separate-confinement-heterostructure, single-quantum-well diode laser has been fabricated on a Si substrate using a single-step metalorganic chemical vapour deposition process. An output power of 30 mW has been obtained under pulsed operation with a peak emission wavelength of 885 nm.<>