Fabrication method for multiple wavelength vertical-cavity emitterarrays by SiNx layer thickness control

We report very narrow and equally spaced eight-channel multiple-wavelength vertical-cavity emitter arrays emitting from 855 to 862 nm with the average spacing of 0.91 nm. For the postgrowth wavelength adjustment, a binary-coded multistep ion beam etching technique is applied to control the thickness of a SiN_x tuning layer located on the first Al_0.15Ga_0.85As quarter-wave layer above the active region. Our result indicates the possibility of the precisely spaced vertical-cavity surface-emitting laser arrays using this kind of postgrowth wavelength adjustment technique     

Realization and performance of as-fabricated SGDBR multiwavelengthlaser arrays

For simplifying the fabrication and operation of multiwavelength laser arrays, sampled grating distributed Bragg reflector (SGDBR) lasers are utilized to form the arrays, where the two SGDBR mirrors of each laser are fabricated on waveguides of different thicknesses. Fabrication of such laser arrays requires a single step of holographic exposure to realize the gratings. The lasers in an array can output wavelength combs of narrow wavelength spacing without the necessity of coarse tuning to the mirrors. We demonstrate monolithically integrated 16-wavelength laser arrays of which the wavelengths are aligned to the International Telecommunication Union grid with single-electrode operation     

Resonant cavity-enhanced InGaAs-AlGaAs heterojunctionphototransistors with an optical design for high uniformity and yield

We present uniformity data on resonant cavity-enhanced InGaAs-AlGaAs heterojunction phototransistors (HPT's) with an optical design that promotes high uniformity and yield. The HPT's operate in the wavelength region where the GaAs substrate is transparent and the data show the HPT's to be suitable for vertical integration with optical emitters or modulators to form two-dimensional arrays of smart pixels operating in transmission mode. The absorbing region of the HPT consists of an InGaAs multiple-quantum-well structure where the quantum wells (QW's) have been distributed to make the total absorption in the cavity insensitive to growth variations as well as the spatial matching of the standing wave and absorbing QW's. Theoretically, we estimate the absorption to be 39%±1% of the incident optical power, even at wafer nonuniformities of 12.5%. With these nonuniformities, the resonant wavelength moves ±25 nm, making postgrowth tuning of the wavelength necessary. Experimentally, we show postgrowth tuning of the resonance wavelength without loss in uniformity. The arrays have good uniformity as well as very high responsivities. The average responsivity is 160 A/W ±15% from 927-955 nm. The standard deviation of a typical array is 0.5 nm in resonant wavelength and about 5% of the average responsivity. The difference between maximum and minimum values for an array is typically 3 nm in resonant wavelength and ±10% of the average responsivity     

Sampled grating DBR laser arrays with adjustable 0.8/1.6 nmwavelength spacing

The difficulty in fabricating multiwavelength laser arrays with uniform wavelength spacing is overcome by using sampled grating distributed Bragg reflector (DBR) lasers as the constituent of a laser array. The sampling periods of the DBR mirrors are varied from laser to laser to provide reflection combs with different spacings in wavelength. Arrays of twelve lasers have been successfully fabricated with a single holographic exposure step. The wavelength spacing among the lasers can be adjusted to be around 0.8 or 1.6 nm with a simple tuning mechanism     

MODIFICATION OF ABSORPTION SPECTRUM OF GaAs/AlGaAs QUANTUM WELL INFRARED PHOTODETECTOR BY POSTGROWTH ADJUSTMENT

IntroductionSince 1980s,the infrared detector based on inter-subband transitions in quantum well(QW)systems,called the quantum well infrared photoconductor(QWIP),has been studied and developed extensivelyand successfully[1].Quantumwell intermixing(QWI)tec…     

Densely packed pie shaped vertical-cavity surface-emitting laserarray incorporating a tapered one-dimensional wet oxidation

Wavelength-division-multiplexing (WDM) photonic integrated emitter (PIE) vertical-cavity surface-emitting laser (VCSEL) arrays are fabricated using a post growth wet oxidation technique. High-density integration of WDM VCSEL arrays is possible by combining the technique of one-dimensional oxidation and large-scale tapered oxidation. Eight channels are integrated into a circle of 60 μm in diameter. Seven channels are found to operate as lasers. The lasing wavelengths range from 823 to 836 nm corresponding with the distance between the VCSEL mesa and the tuning trench. The successful demonstration of incorporating wet oxidation into the wavelength control of the PIE VCSEL array opens a new way of fabricating mask-defined densely packed WDM VCSEL arrays     

MODIFICATION OF ABSORPTION SPECTRUM OF GaAs/AIGaAs QUANTUM WELL INFRARED PHOTODETECTOR BY POSTGROWTH ADJUSTMENT

Quantum well intermixing techniques modify the geometric shape of quantum wells to allow postgrowth adjustments. The tuning effect on the optical response property of a GaAs/AlGaAs quantum well infrared photodetector (QWIP) induced by the interdifussion of Al atoms was studied theoretically. By assuming an improvement of the heterointerface quality and an enhanced Al interdiffusion caused by postgrowth intermixings, the photoluminescence spectrum shows a blueshifted, narrower and enhanced photoluminescence peak. The infrared optical absorption spectrum also shows the expected redshift of the response wavelength. However, the variation in the absorption peak intensity depends on the boundary conditions of the photo generated carriers. For high-quality QWIP samples, the mean free path of photocarriers is long so that the photocarriers are largely coherent when they transport across quantum wells. In this case, the enhanced Al interdiffusion can significantly degrade the infrared absorption property of the QWIP. Special effects are therefore neededto maintain and/or improve the optical properties of the QWIP device during postgrowth treatments.     

Dynamic single-transverse-mode properties of varying ridge width DFB laser arrays

Controlling the lasing wavelength by varying the ridge width is a simple and versatile technique for realizing practical WDM laser arrays. The purpose of this letter is to report the dynamic transverse mode properties of such laser arrays. We show that it is possible to maintain single-mode lasing even for ridges wide enough to support multiple transverse modes. As a result, we were able to increase the tuning range in the array without introducing any detrimental effects on their single-mode properties.     

Stacked polymeric multimode waveguide arrays for two-dimensional optical interconnects

Two-dimensional (2-D) polymeric multimode waveguide arrays with two reflection-mirrors have been fabricated for optical interconnects between 2-D arrayed vertical-cavity surface-emitting lasers and detectors. Contact printing lithography was adopted for simple and low-cost process using ultraviolet-curable epoxy-based polymers. Fabricated waveguides were diced of the same size and stacked one by one with lateral positional errors less than /spl plusmn/20 /spl mu/m. Two kinds of mirrors were fabricated: single-reflection mirror and double-reflection mirror. Double-reflected mirrors resulted in lower losses with 1.2 dB than single reflected mirrors with 2.1 dB. The average insertion losses of 16-channel arrayed waveguides with two single-reflection mirrors and with two double-reflection-mirrors were measured to be 6.1 and 4.4 dB for 6-cm-long waveguides at a wavelength of 830 nm, respectively. The crosstalk between the waveguides was less than -25 dB. The characteristics of the waveguide arrays are good enough for applications to optical interconnects.     

High damage threshold HfO2/SiO2 multilayer mirrors deposited by novel remote plasma sputtering

Sputtering deposition coatings offer significant advantages on electron beam (EB) deposition, including high packing density, environmental stability and extremely low losses. But the inherent high compressive stress affects its application in high power laser system. This paper describes the technical feasibility of high damage threshold laser mirrors deposited by a novel remote plasma sputtering technique. This technique is based on generating intensive plasma remotely from the target and then magnetically steering the plasma to the target to realize the full uniform sputtering. The pseudo-independence between target voltage and target current provides us very flexible parameters tuning, especially for the films stress control. Deposition conditions are optimized to yield fully oxidized and low compressive stress single layer HfO2 and SiO2. The high damage threshold of 43.8 J/cm2 for HfO2/ SiO2 laser mirrors at 1064 nm is obtained. For the first time the remote plasma sputtering is successfully applied in depositing laser mirrors with high performance.     

可调谐单频掺镱光纤DBR激光器

对分布布拉格反射(DBR)的透射特性进行了分析,制作了一个单频窄线宽掺镱光纤DBR激光器.在977 nm半导体激光器泵浦下,在1052.5 nm波长处输出功率可达4 mW,线宽小于8 MHz(受测量仪器分辨率限制).采用弧形梁调谐光纤光栅,实现了DBR光纤激光器在单纵模工作状态下的连续调谐,调谐范围可达20.4 nm(1036.1～1056.5 nm),并研究了调谐对激光器的泵浦阈值和斜率效率的影响.     

Multiple-wavelength vertical-cavity surface-emitting laser arrays with a record wavelength span

Multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) arrays are fabricated using a modified patterned-substrate growth technique in a molecular beam epitaxy (MBE) system. We achieved a large lasing wavelength span of 62.7 nm and highly uniform threshold currents with an average of 2.16/spl plusmn/0.81 mA. High repeatibility of wavelength spacing between 15 arrays with sharp wavelength shift rate 117.14 nm/mm is achieved.     

Wavelength-graded horizontal cavity laser array with postgrowthadjustment of wavelength

Wavelength-graded emission from a visible red GaInP-AlGaInP laser diode array has been achieved with the contradirectional surface-mode coupling technique. The wavelength control is attained by postgrowth adjustment of the thickness of the surface waveguide. The horizontal cavity lasers show both edge and surface emission (beam divergence 0.12°). The thermal red-shift of the wavelength is 0.028±0.002 nm/K. They show single-mode emission with a typical spectral linewidth of 0.09 nm and a sidemode suppression ratio up to 29 dB. The wavelength spacing between the individual lasers is 0.76±0.08 nm yielding a total range across the array of 5.4 nm (from 681.5 to 686.9 nm)     

Extended tuning range in sampled grating DBR lasers

The authors demonstrate, for the first time, successful implementation of a distributed Bragg reflector laser with two sampled grating mirrors, which they previously predicted should give tuning range in excess of 50 nm. This device uses a uniform grating pitch throughout the structure, and relies on the same fabrication technology as a standard DBR laser. Initial results show 57 nm of mathematical tuning at 1.475 μm with side-mode suppression ratio (SMSR)>30 dB over much of the tuning range. The observed change in operating wavelength versus mirror currents along with below threshold spectra agree with theoretical expectations     

Design of low-voltage CMOS continuous-time filter with on-chipautomatic tuning

A technique for designing a low-voltage continuous-time active filter is presented in this paper. In this technique, current sources are added to the inverting or noninverting op-amp terminals such that the op-amp input common-mode voltages can be set close to one of the supply rails to allow low-voltage operation. An automatic frequency and Q tuning technique is proposed for tuning the active filter using programmable capacitor arrays (PCAs). The proposed tuning technique does not require any peak detectors, which are difficult to implement at a low supply voltage. Instead, it uses a few analog comparators, a digital comparator, and a few binary counters to adjust the PCAs. To demonstrate the proposed techniques, a 1-V 1-MHz second-order filter fabricated in a conventional 1.2-μm CMOS process is presented. For a 5-kHz input signal, the filter achieves a THD of -60.2 dB for a peak-to-peak output voltage of 600 mV. The frequency tuning range is between 585 kHz and 1.325 MHz. The measured power consumption for the filter alone consumes about 0.52 mW and for the entire system consumes about 1.6 mW for a supply voltage of ±0.5 V     

Extended Tunability in a Two-Chip VECSEL

We demonstrate a widely tunable vertical-external-cavity surface-emitting laser (VECSEL) with a W-shaped cavity, in which two VECSEL chips serve as fold mirrors and a birefringent filter is inserted at Brewster's angle. These two chips provide much higher modal gain and broader bandwidth of the gain than a single chip does, enhancing the VECSEL tuning range and reducing the variation of tunable output power with the tuned wavelength. This two-chip VECSEL configuration makes it possible to shape the modal gain spectra of the laser or to manipulate the tuning curve of the laser by two different chips with certain gain peak detuning (offset). Multiwatts high-brightness linearly polarized output with a tuning range of 33 nm is demonstrated in such a two-chip VECSEL     

连续钛宝石激光器波长调谐特性及斜效率的测量

采用四镜折叠驻波腔，以氩离子激光器的可见多谱线输出纵向激励，用国产钛宝石激光棒实现了连续激光运转。使用三套腔镜得到的波长调谐范围分别为６８０～７６０ｕｍ、７３０～８４０ｕｍ、９７０～１０１０ｎｍ，峰值波长约为７８０ｕｍ。当输出透射率为１１．７６％、泵浦功率约１０．０Ｗ时，获得７８０ｕｍ波长的激光最大输出功率约２．３５Ｗ，斜效率为３３．４９％。     

Tuning Bragg wavelength by writing gratings on prestrained fibers

Bragg gratings at a specific wavelength are made using an excimer KrF laser and a phase mask. The wavelength can be varied for fine tuning and multiplexing applications by straining the optical fiber during UV illumination. When the strain is removed, the grating formed is at a smaller wavelength than that dictated by the phase mask for the unstrained fiber. This technique was demonstrated by writing two gratings located at the same point in the optical fiber. The transmission from the first grating was used as a means for in situ absolute wavelength tuning. The second grating made with approximately 0.2% axial strain was at 1534.54 nm. Once the grating was made, the strain was removed from the fiber leaving the second grating tuned to 1532.04 nm, a wavelength shift of 2.5 nm     

Element spacing limitations of Dolph-Pritchard optimum endfire arrays

It is generally accepted that the Dolph-Pritchard technique for computing optimum or Chebyshev radiation patterns for single-lobe endfire arrays is valid for any array element spacing less than one-half wavelength. However, it can be shown that multiple-lobe radiation patterns will be obtained using this technique for element spacing less than one-half wavelength. A maximum element spacing for single-lobe radiation patterns can be derived, and this spacing is a function of the major-lobe-to-sidelobe amplitude ratio as well as the order of the Chebyshev polynomial. In general, for large amplitude ratios this maximum spacing approaches one-quarter wavelength.     

High Rejection Ratio Tilted-Mirror Interferometer

This paper covers the tilted-mirror interferometer, which is an improvement of the similar configuration with parallel mirrors in several important parameters, such as: rejection ratio increase from 26 to 45 dB, the slopes of the transmission peaks increases from 4 to 40 dB/nm, and decreases several times the bandwidth at 3 dB. All the other parameters of nonmodulated light, such as 240-nm tuning range, tuning speed of 2 s/nm, tuning accuracy of 1 pm, 1-dB insertion loss, 0.2-dB flatness, 0.15-dB polarization-dependent loss are the same as in the configuration with parallel mirrors. The experiments have shown that the version with tilted mirrors has 80-nm/m tuning sensitivity to the gap change, slightly better than the configuration with the parallel mirrors.