The paper describes a monolithically integrated planar microlens array and its applications. An ion exchange technology is applied to realize the microlens array with diameters of 10 - 1000 pm and N.A. of 0.25. Applications to optical fiber communications, combinations with CCD arrays and optical computing are demonstrated.
Detection and characterization of high speed x-ray, gamma ray or particle beam signals in an intense radiation environment pose problems for conventional electronic systems since the presence of the intense radiation field interferes with the electronic systems used in the diagnostics. It is therefore highly desirable to remote the diagnostic equipments away from the radiation environment, where radiation sensors convert the radiation signals into electrical signals being transported to the remote location. However, the transportation of these high speed signals with gigahertz bandwidths is not a trivial matter, due to its very high bandwidth and its total immunity to electromagnetic interference. It would therefore be necessary to convert the electrical signal from the radiation detector into an optical signal for subsequent transportation. This is schematically illustrated in Fig. 1, where the transmitter refers to an electrical-to-light conversion device, and the optical fiber can be many kilometers long before affected by bandwidth limitations. Semiconductor lasers with gigahertz modulation bandwidths have been developed in recent years for high speed analog signal transmission, and are ideal for the present application. Since these semiconductor lasers as well as the radiation detectors are fabricated from GaAs based compounds, it is logical to consider integrating them into a single monolithic device. The integrated device takes the form shown in Fig. 2, which shows a photo (radiation) detector connected in series with a laser diode. The DC bias current is for biasing the lasing into the linear region above lasing threshold, and the signal generated from the photoconductor modulates the current into the laser thereby modulating the optical output.
Lenses and mirrors of micrometer scale have been fabricated in the InGaAsP/InP heterostructure material. These microoptical components include two-dimensional flat and cylindrical end-mirrors which are a part of edge-emitting laser cavities, integrated 45° beam-deflectors which direct the output beam from edge-emitting lasers to emit perpendicular to the substrate surface, and large-numerical-aperture refractive and diffractive lenses for collimating light from the diode lasers. They were fabricated by etching, using both wet-chemical and dry processes, lithographically defined patterns. In many cases a mass-transport process was also used to smooth the etched structures.
A microlens fabrication process is described which is based on commercially available IC processing materials. The lenses are formed on top of circular pedestals by melting a photoresist developed in a suitable pattern. Due to surface tension forces melting leads to formation of a spherical surface which is pinned by the sharp edge of the pedestal. The process gives microlenses of excellent quality which show diffraction limited resolution.
This paper proposes a new cost effective method for the testing of thin film magnetic recording heads. The primary advantage of this technique is that through use of magneto-optics, test can be carried out at the wafer level and thereby eliminate defective heads before additional manufacturing costs are added to the product.
The evolution of optical techniques for use in electronic and optoelectronic computers is considered. Special emphasis is placed on the interconnection properties of optical systems. The development of a new class of fiber optic based logic devices that are capable of operating in a high power-bandwidth regime is discussed.
A short survey of past experimental results is presented along with new investigative data, mathematical and physical response models and a comparison of the nuclear effects compatibility of fiber and integrated optic guided wave structures. The disparity in radiation resistance between optical fibers and guided wave structures is discussed and predictions are offered on the impact that these differences may have on influencing the eventual development of totally integrated radiation resistant structures.
Proc. SPIE 0898, On The Noise Power In 2D Op Toelectronic Devices Made Of A[sub]3[/sub][sup]II[/sup] B[sub]2[/sub][sup]V[/sup] Type Of Optoelectronic Materials, 0000 (2 June 1988); doi: 10.1117/12.944562
In recent years there has been considerable interest in studying the noise power of the 2D optoelectronic devices under different physical conditions. Besides, the connection of the noise power with the Einstein relation for the diffusivity-mobility ratio of the carriers in optical materials and its influence that further integrate electronic functions with optical devices have extensively been investigated in the literature. Keeping this in view, an attempt is madp fox the first time to study the noise power in 2D optoelectronic devices made of AIB9v type of degenerate opto-electronic materials having non-parabolic and non-dtanaard energy bands. Introduing the anisotropic crystal potential to the Hamiltonian we have first lolerived an E-k dispersion relation of the carriers in the bulk specimens of "B2 v type of opto-electronic materials within the framework of k . p formalism, according to which the conduction band corresponds to a single ellipsoid of revolution at the zone center in k-space by incorporating the anisotropies in the momentum-matrix element and the spin-orbit splitting parameters, respectively, since the anisotropies in the two afore mentioned band parameters are significant physical features of the above class of materials. 'de have then formulated the 2D noise power in the presence of an infinitely deep 1D square potential well leading to the quantization of the wave vectors of the carriers which produces a discrete energy spectrum. It is found, taking n-Cd1P2 as an example which is being currently used as optoelectronic materials and photod6tectors in the near infrared region, that the noise power in 2D optoelectronic devices increases with decreasing film thickness, for a fixed electron concentration, and also increases with increasing surface electron concentration corresponding to a given film thickness. The theoretical formulations are in excellent agreement with the experimental results and the corresponding well-known results for standard devices are also obtained from the expressions derived.
A number of laser and non-linear optical technologies are converging on commercial designs. High power laser diodes and non-linear materials are being incorporated in prototype lasers, many of which will become commercially available products during the next 1-5 years. This paper will review the output characteristics of such lasers. Lasers which will be discussed include direct doubling of laser diodes based on proton exchanged lithium niobate, fiber lasers, frequency doubled diode pumped Nd:YAG lasers, and sum frequency mixed Nd:YAG lasers. Such lasers are capable of providing milliwatt output powers in the green and/or blue spectral regions.
Nonlinear optical processes permit the design of miniaturized blue - green laser devices that are pumped by near-infrared sources such as GaAIAs diode lasers. Frequency upconversion of infrared pump light can be achieved by processes that use the nonlinear susceptibility of noncentrosymmetric materials for second harmonic generation or sum-frequency mixing. In addition, two-photon excitation mechanisms including sequential two-step absorption and energy-transfer upconversion can be used to pump visible solid-state lasers with infrared light. The operation of several nonlinear laser devices in the blue - green spectral region has been demonstrated. Intracavity frequency mixing of a 1064-nm Nd:YAG laser and its 809-nm pump source resulted in efficient generation of 459-nm radiation using KTi0PO4 as the nonlinear material. Intracavity frequency doubling of a diode-laser pumped 946-nm Nd:YAG laser was used to generate 473-nm radiation. Two-photon-pumped upconversion lasing at 550nm has been demonstrated in YA103:Er3+ and YLiF4:Er3+ at temperatures <90K using infrared cw dye lasers near 800nm as pump sources.
Intracavity upconversion of an 808-nm laser diode to 459 nm using KTP in a diode-pumped Nd:YAG laser produced tens of microwatts CW and modulated blue output. Milliwatt CW outputs were achieved with a dye laser. Modulation will be discussed as will the possibility of similar locally tunable systems throughout the visible.
A compact, blue light source using a GaAlAs laser diode and a guided-wave frequency doubler is demonstrated at room temperature. The 0.84pm wave from the laser diode is frequency doubled using the Cherenkov radiation scheme in a proton-exchanged LiNbO3 waveguide. The conversion efficiency of the frequency doubler is 1.6%. Maximum harmonic output power of 1.05mW at 0.42pm was achieved for diode laser output power of 120mW, for a total conversion efficiency of 0.9%. -
In the early work on compact, air-cooled, metal/ceramic, argon ion lasers, the emphasis was on refining designs for vacuum integrity, thermo-mechanical stability, and processing technology for relatively high volume production. As these issues are now well in hand and many thousands of these lasers are in the hands of the manufacturers customers, people are exploring the limits of their use in systems. The technical issues now are those of performance characteristics related to specific applications or proposed applica-tions. Some of these relate to what extent can the internal mirror, internal resonator design in metal/ceramic ion lasers be scaled. Improvements in optical coating technology and modification in the optical cavity and plasma tube design have allowed the air-cooled ion laser to be a more versatile, multi-wavelength or single wavelength source.
A gain-guide tapered stripe laser was fabricated by metalorganic chemical vapor deposition. Improved characteristics, such asoa low threshold current of 48mA, a maximum temperature for continuous wave operation of 81C and an small astigmatic difference of 25pm, have been achieved. Sixteen cdevices have been operating without significant degradation for more than 5000 hours at 50C with a constant output power of 3mW. A high output power of 250mW has also obtained by the broad stripe laser.
Transverse mode stabilized AIGaInP visible light laser diodes are described and their high power operations are discussed. The laser structure applied for transverse mode stabilization is a ridge shape self-aligned structure, which is designed taking fabrication reproducibility into consideration. A very thin GaInP etching stopper layer is introduced in order to enable easy and accurate control of the dimensions of the self-aligned structure. Threshold current is about 30-50mA. Over 10mW output power is obtained for LDs with as-cleaved facets. Output power is limited by COD (catastrophic optical damage). COD power level under continuous-wave (cw) operation is estimated to be 1.4-1.7MW/cm2. After facet-coating, a stable fundamental mode operation, up to 20mw (cw), and maximum output power 31mW (cw), which is limited by COD, have been obtained. The lasing wavelength is 670nm.
Performance data for a laser diode pumped cw Nd:BEL laser is presented. Two phased laser diode arrays are used as the pump source, each emitting 500 mW. The heat sink for the arrays is temperature controlled to allow for wavelength tunability. A Nd:YAG rod was pumped under similar conditions and the results are compared. Although the absorption bandwidth for Nd:BEL is substantially broader than for Nd:YAG, the Nd:BEL was found to have a higher threshold for lasing. Both rods gave slope efficiencies of 42%. The dependence of the output power on output mirror reflectivity was measured, with Nd:BEL showing a greater sensitivity to reflectivity than Nd:YAG. The optimum reflectivities were found to be .98 and .97 for Nd:BEL and Nd:YAG respectively. The maximum TEMOO cw power achieved for each rod at these reflectivities was 250 mW for Nd:BEL and 283 mW for Nd:YAG. The observed electrical to optical conversion efficiency was factored into a product of analytic component terms and excellent agreement was found between observed and calculated efficiencies. We conclude that under the conditions used in this work, both BEL and YAG hosts perform comparably.
Experimental and theorectical studies of diode-pumped Tb:NdYAP system are performed. A generalized model which governs system key parameters of spatial mode matching, beam divergence, reflectivity, cavity loss, slope efficiency and threshold power is presented and analytical results for the mode overlap function are calculated. Experiments are carried out in an end-pumped configuration, where a YAP rod is pumped in the a-axis direction. The output efficiency for emission at 1079 nm is measured. Applications provided by the aniso--tropic feature of the YAP rod are explored for various crystal orientations and the polarizations of the emission lines at 1064 nm and 1079 nm.
Diode-pumped solid state lasers are efficient and compact sources of coherent IR radiation, but for many applications short wavelength visible sources are desired. Intracavity frequency doubling is a proven method of efficient conversion of these lasers to the visible, but generally results in deeply amplitude modulated output. An alternative approach is external cavity frequency doubling to provide stable single-axial-mode output at the second harmonic. We have used external cavity frequency doubling to generate 56% second harmonic conversion efficiency of a 53 mW, cw, diode-laser-pumped Nd:YAG oscillator. A monolithic cavity of MgO:LiNb03 resonant at the fundamental was used to generate the 30 mW of single axial mode 532 nm radiation.
Q-switching of diode-pumped Nd:YAG and Nd:YLF at 1.064, 1.047, and 1.321 microns is discussed. Single frequency versions have also been demonstrated. A simple 3 longitudinal mode rate-equation model is used to predict pulse stability. Wavelength extension by frequency doubling and fiberoptic Raman shifting is discussed, and several applications are described.