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An autofocus circuit, based on measurement of the high spatial frequency image components, was designed for automated microscopic scanning of biological specimens. By careful consideration of the system transfer function, elimination of video end-of-line filter artifacts, correction for illumination instability, and incorporation of autogain, the focus measurement circuit attained the sensitivity and dynamic range necessary for robust operation even at the extremes of biological specimen detail encountered in exhaustive raster scans of thousands of fields. This new circuit exhibited a 25-fold improvement in dynamic range over a previous analog implementation, matched real-time digital performance at an order of magnitude lower cost, resulted in autofocus precision of 56 nm (or 10-fold better than the depth of field of the objective) in scanning experiments comprising over 10 000 microscope fields, and tracked focus at scanning speeds of up to 3.45 fields/s. Focus was correctly maintained in these scanning experiments without additional compensation for low-detail images. This circuit makes possible the widespread inclusion of high-performance autofocus as a low cost option in video microscopy systems.

Image-based autofocus determines focus directly from the specimen (as opposed to reflective surface positioning with an offset), but sequential acquisition of a stack of images to measure resolution/sharpness and find best focus is slower than reflective positioning. Simultaneous imaging of multiple focal planes, which is also useful for 3D imaging of live cells, is faster but requires complicated optics. With color CCD cameras and white light sources commonly available, we asked if axial chromatic aberration can be utilized to acquire multiple focal planes simultaneously, and if it can be controlled through a range sufficient for practical use. For proof of concept, we theoretically and experimentally explored the focal differences between three narrow wavelength bands on a 3-chip color CCD camera with and without glass inserts of various thicknesses and dispersions. Ray tracing yielded changes in foci of 0.65–0.9 μm upon insertion of 12.5-mm thick glass samples for green (G, 522 nm) vs. blue (B, 462 nm) and green vs. red (G-R, 604 nm). On a microscope: (1) With no glass inserts, the differences in foci were 2.15 μm (G-B) and 0.43 μm (G-R); (2) With glass inserts, the maximum change in foci for G vs. B was 0.44 μm and for G vs. R was 0.26 μm; and (3) An 11.3 mm thick N-BK7 glass insert shifted the foci 0.9 μm (R), 0.6 μm (G), and 0.35 μm (B), such that the B and R foci were farther apart (2.1 μm vs. 1.7 μm) and the R and G foci were closer together (0.25 μm vs. 0.45 μm). The slopes of the differences in foci were dependent on thickness, index of refraction, and dispersion. The measured differences in foci are comparable to the axial steps of 0.1–0.24 μm commonly used for autofocus, and focal plane separation can be altered by inserting optical elements of various dispersions and thicknesses. By enabling acquisition of multiple, axially offset images simultaneously, chromatic aberration, normally an imaging pariah, creates a possible mechanism for efficient multiplanar imaging of multiple spectral bands from white light illumination. © 2009 International Society for Advancement of Cytometry

The design, fabrication and performance of an integrated optical R.F. spectrum analyzer is described. The device consists of an injection laser, the IO substrate and a photodiode array. It operates over a frequency band-width of 400 MHz centered at 600 MHz and with a complete frame time of 2 mu sec. An R. F. input signal dynamic range in excess of 20 dB has been measured.

The spurious-free dynamic range (SFDR) of an InGaAsP-InP Franz-Keldysh effect (FKE) waveguide modulator is studied. Low-biasing the FKE modulator is shown to enhance the SFDR by 22 dB with a 3-dB optical power penalty. Polarization-independent RF operation is also obtained with low bias. At 2 mA photocurrent, the simulated narrowband and broadband SFDR are, respectively, 127 dB and 104 dB in a 1-Hz bandwidth. The measured result projects a narrowband SFDR of 129 dB-Hz/sup 4/5/ at this photocurrent. >

In this paper, the fabrication, frequency response, and saturation characteristics of a waveguide pin photodiode made from double heterostructure InGaAs/InP materials are presented. The detector is designed for operation at optical wavelengths ranging from 1.3 to 1.5 /spl mu/m. The materials are grown using a low pressure, organo-metallic vapor phase epitaxial reactor. Due to the use of a vent-run manifold and growth interruption at the heterointerface, high quality detector material is obtained. >

Laser mode-locking is an effective modulation technique which can be used in fiberoptic link applications. In a semiconductor laser, active mode-locking can be achieved through the direct modulation of the laser at the cavity resonant frequency. If the modulation frequency is detuned from this condition, large optical intensity fluctuations can occur, which can cause a significant degradation in the noise figure of the laser, and consequently in the noise figure of the overall link. In this paper, we investigate the consequence of frequency detuning an actively mode-locked external-cavity semiconductor laser. We experimentally demonstrate the existence of chaos in a mode-locked laser upon frequency detuning. To our knowledge, chaotic instability in an actively mode-locked semiconductor laser has not been reported. >

Simultaneous multi planar microscope imaging enables parallel computation of autofocus for high-sped image cytometry. Although image cytometry exhibits many potential advantages over flow cytometry, substantially slower speed has limited use to fewer applications. In commercial image cytometry instruments, long scanning times have typically been circumvented by identification of small areas of interest during high speed, low resolution scans for subsequent analysis at high resolution. This two-pass strategy of analyzing only a few cells at high resolution is a disadvantage and often cannot be used at all where dim fluorescence demands higher numerical aperture (NA) objectives. Continuous stage motion synchronized with line array or time-delay-and-integrate (TDI) CCD image acquisition is capable of increasing scan speed by an order of magnitude or more, but until recently lacked the autofocus required for higher resolution objectives where depth of field is about the thickness of a cell monolayer. Here we describe an improved design for simultaneous multi planar acquisition and on-the-fly autofocus. This new system replaces more complicated and less light efficient fiberoptic imaging bundles with beamsplitters and mirrors. This new image-splitting design also enables addition of magnification correction optics not easily added to the earlier fiberoptic version. The result is a simplified, high sensitivity, magnification-matched, parallel multi planar acquisition module containing an array of CCD sensors for high-speed focus tracking and 3D imaging.

A four-layer asymmetric waveguide structure using a nonabsorbing 1.08 eV bandgap InGaAsP waveguiding layer has been studied for high saturation power, high speed waveguide photodiode operating at 1.32 micrometers wavelength. A peak photocurrent of 32 mA corresponding to an optical power of 76 mW has been obtained for 40 GHz waveguide photodiode.

Chaotic stability of external cavity semiconductor laser under modulation is examined both theoretically and experimentally. When the modulation frequency is detuned below the cavity resonant frequency, the simulations show a two-frequency to three-frequency route to chaos, as depicted by the power spectrum and time series of the laser emission at different stages of detuning. This agrees with experimental observations of 1.3 micrometer wavelength distributed feedback (DFB) laser and ridge waveguide (RW) InGaAsP laser. The phase-space attractor of both DFB and RW lasers have well-defined structures at broadband chaotic state, which signifies the presence of dynamical determinism in this state.

High-frequency and high-responsivity photodetectors which possess a high saturation intensity are needed for high performance analog fiber optic links. We report the results of a high saturation intensity InGaAs/InP PIN waveguide photodetector. At an optical wavelength of 1.3 micrometers , the detector has a responsivity of 0.5 A/W and a flat frequency response from 800 MHz to 20 GHz. With a bias of -4 V, the normalized frequency response of the detector remains unchanged when optical powers up to 10 mW are incident on the detector. An initial linearity measurement is made by measuring the linearity of a fiber optic link which uses the detector with a DC photocurrent of 140 (mu) A as the receiver. The linearity of the link is limited by the modulator of the link and there is no detectable nonlinearity introduced by the detector.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A fully packaged and connectorized 1.32 micrometers InGaAsP electroabsorption modulator for analog fiber optic link applications is described. This Franz-Keldysh effect modulator has a 3-dBe bandwidth exceeding 20 GHz, a fiber-to-fiber optical insertion loss of less than 9 dB, and a high modulation efficiency (equivalent switching voltage less than 10 V). A fiber link spurious free dynamic range of greater than 100 dB in a 1 Hz bandwidth is achievable using this modulator, which makes it attractive for Navy shipboard applications.

Autofocus is a critical aspect of any automated microscopy application. Here we report on the successful exploitation of chromatic aberration to speed autofocus for biological microscopy. Using pairs of lenses aligned nominally as infinite conjugates, the chromatic aberration produced by a microscope can be manipulated to achieve multiplanar imaging covering a wide range of spacings. Using both three-chip CCD and Bayer-array color cameras, chromatic aberration-based multiplanar imaging is used to reduce by a factor of 3 the number of mechanical movements of the biological sample necessary to determine best focus. Chromatic aberration-based autofocus is validated using a 20×0.75 NA objective while scanning over 6000 fields of National Institutes of Health 3T3 cells cultured on a coverglass. The combined precisions (standard deviations) of 23.7 nm for a three-chip CCD camera and 23.3 nm for a Bayer-array camera are obtained. These precisions are approximately 1/20th of the depth of field of the objective.

A 1.3-micron wavelength optical transmitter system with a 2-GHz bandwidth centered at 20 GHz has been implemented by actively mode-locking a semiconductor laser diode and then modulating the signal externally. The performance of a link using this transmitter over a 2-km fiber is evaluated. A hybrid package is developed for a mode-locked laser submodule operating at 15 GHz.

A compact 5-bit MMIC phase shifter has been developed utilizing EEl' switches and coplanar waveguide delay lines. The device has constant time delay over a bandwidth of more than 18% with an accuracy of±1 .2 Ps at X-band (±5°). An 1 1 .5 GHz version has less than 1 2 dB of insertion loss for any of its 32 states and an overall chip dimension of 2.25 x 2 .50 mm. A 20 GHz version has less than 1 1 dB of insertion loss and an overall chip dimension of 2.0 x 3.0 mm. Unit-to-unit variation in absolute time delay is less than 2 ps across two wafer lots andfour wafers.

We demonstrate a 1.3 micron wavelength optical transmitter system with a 20 GHz RF center frequency and 2 GHz bandwidth. We accomplish this by actively modelocking a semiconductor diode laser at 14 GHz; the modelocked signal is then externally modulated between 5 GHz and 7 GHz, using a lithium niobate based Mach-Zehnder modulator. We show a hybrid prototype package for the modelocked laser source.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The measurement of the relative intensity noise (RIN) of a ridge waveguide laser and a distributed feedback laser under CW, external cavity, direct modulation, and modelocking conditions is presented. The purpose is to determine the relative noise performance of modelocked laser diodes. The results indicate that the RIN of modelocked lasers are comparable to CW lasers but lower than both external cavity lasers (optimized for modelocking but without the applied RF) and directly modulated lasers; the difference can be as much as 5 optical dB. The microwave carriers produced optically by the direct modulation and modelocking of laser diodes are also compared. The comparison determines that modelocked lasers produce less noisy and more RF power efficient microwave carriers. However, no difference in microwave linewidth is detected within the limit of the resolution bandwidth of the detection system.

The performance of the high speed InGaAsP ridge waveguide lasers and the GaAlAs single-mode lasers operating as a micromixer have been investigated by using a circuit model derived from the iterative method and device rate equations. The laser mixer has many advantages over the conventional microwave mixer, including: high conversion gain, wide dynamic range, low noise figure and high local oscillator/intermediate frequency (LO/IF) isolation. The analytic results also indicate that the heterodyne microwave fiber optic link using a laser mixer provides the advantages of system simplicity, cost-effectiveness and improved system signal-to-noise ratio (SNR) than the conventional microwave fiber optic links. System SNR of two fiber optic links were measured: a 12 GHz link with 70 MHz IF has a SNR of better than 120 dB/Hz and a 26.5 GHz up-converted link has a SNR of 100 dB/Hz, without laser diode RF impedance matching. Other system applications of the laser mixer are also presented.

We examine experimentally the consequence of frequency detuning an actively mode-locked external-cavity semiconductor laser from resonance. We observe a transition of the laser system from a periodic oscillation to a nonperiodic state with broadened spectral tones. By estimating the fractal dimension of the corresponding phase-space attractors, we show the presence of low-dimensional chaos. The route to chaos is a well-defined regime of three-frequency quasi-periodicity preceded by a two-frequency quasi-periodicity.

The high frequency saturation characteristics of an InGaAs/InP waveguide pin photodetector are measured. At a wavelength of 1.3 μm, the detector has a responsivity of 0.5 A/W and a flat frequency response from 800 MHz to 20 GHz. With a bias of −4 V, the normalised frequency response of the detector remains unchanged when optical powers up to l0 mW are incident on the detector.

An InGaAs/InP rib-loaded waveguide pin, photodetector integrated with a microwave coplanar waveguide transmission line on a semi-insulating InP substrate is demonstrated. The detector has a 3 dB frequency response in excess of 20 GHz. The DC responsivity of the waveguide photo-detector remains constant at 0.21 A/W over a range of incident optical powers from 400 μW to 20 mW.

An analysis is given of the radio- and audio-frequency modulation method employed in microwave spectroscopy. The results of the theory are compared with measurements taken on a 8 mm microwave spectrometer and are found to be in close agreement. The calculations are extended to include the case where an absorbing gas is enclosed in a resonant cavity.

An attempt has been made to interpret the infra-red spectrum of polythene as the spectrum of an infinitely long chain of CH2-groups. The vibrations of such a chain have been calculated using a potential function which involves valence and angle forces as well as the torsional force resisting a twisting of the C-C bonds. The selection rules and states of polarization of the fourteen possible frequencies are derived. The observed bands are assigned to the calculated vibrations and the force constants are evaluated. It is shown that the oscillations involving the C-C valence force are weakly active in contradiction to the theory In the last section, this activity has been ascribed to the presence of CH3-groups at the ends of the polythene chain.

Many methods have been presented and discussed for the solution of modes and propagation constants of optical waveguides [1,2]. Waveguides normally obtained and used for integrated optics (e.g., titanium indiffused lithium niobate) have index profiles which are anisotropic, of arbitrary cross-section, and of arbitrary index profile. It would be beneficial to require our method to be capable of treating waveguides of this type.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Efforts to improve upon the reported dynamic range of newly developed integrated optical RF spectrum analyzers center about two separate components. One of these is an efficiently coupled, high power, single mode, narrow-beam-spread GaAlAs laser diode and the other is the photodiode array with its associated read-out circuitry. Recent attempts to realize improvements in both of these components are described, as are the design changes in the spectrum analyzer necessitated by the characteristics of available laser diodes.

The operating characteristics of a hybrid integrated optical spectrum analyzer and the results of a design analysis performed to permit the development of an improved device are discussed. The existing device incorporates a LiNbOs substrate, which contains a Ti-indif- fused optical waveguide, two near-diffraction-limited geodesic waveguide lenses, and a two- element surface acoustic wave transducer array, and a butt-coupled photodiode array. The optical source is either an end-fire or butt-coupled laser. This unit has been shown to operate over a 400 MHz bandwidth with a resolution which varies from 5.3 MHz for an optical wavelength of 0.6328 urn to 4.0 MHz for 0.83 ym.IntroductionDuring the past several years considerable effort has been focused upon the development of an integrated optical RF spectrum analyzer (IO SA) . This first 10 device demonstrates the feasibility of applying integrated optics to complex signal processing. 1 Initially, this effort was devoted to the development of individual 10 components such as waveguides, waveguide couplers, broadband surface acoustic wave (SAW) transducers, waveguide lenses, and high speed detector arrays capable of operating over a large dynamic range. Two differ ent waveguide technologies were explored; one using silicon as the substrate material, and the other, lithium niobateThe use of silicon as the substrate material is desirable in that detector arrays can be fabricated such that the waveguided radiation is coupled directly into the detector ele­ ments . 2 , 3 in addition, waveguides on silicon substrate are formed by sputtering a higher index film over a thermally grown Si02 buffer layer grown over the polished face of the silicon. Since such waveguides are fabricated of materials with relatively low optical re­ fractive indices, it is possible to utilize one of many available materials of significant­ ly greater refractive index to fabricate Luneburg waveguide lenses. ^ Such lenses were thought to be advantageous in that the contour and thickness of the sputtered lens material could be controlled to yield a near-diffraction-limited image. Even though analyses indi­ cated extremely tight tolerances of the order of tens of angstroms on the thickness and contour of such sputtered films must be met, this technology was considered desirable since it involved standard processing techniques employed in integrated circuits.The major disadvantage of silicon-based integrated optics technology is the need for a separate piezoelectric material to form the broadband SAW transducer. Several experimental efforts use ZnO as such a piezoelectric material in conjunction with interdigitated metal finger patterns to form electrically efficient SAW transducers . 6 , 7 one such effort result­ ed in transduction which approached the theoretical efficiency limit but it was found that the SAW propagation through both the ZnO and the optical waveguide was significantly more lossy than that observed on single crystal LiNbOs surfaces.As a result of the reported high SAW propagation losses in ZnO and in waveguides sput­ tered on Si substrates, the emphasis shifted toward the use of LiNbO3 as the preferred sub­ strate material. Waveguides are formed in LiNbO3 by Ti indif fusion or by Li20 outdif fusion; the former has been found to provide a more tightly confined waveguide with optical propa­ gation losses of the order of 0.5 dB/cm. Transducers can be easily fabricated on LiNb03 by depositing an interdigitated finger pattern on the waveguide surface because the material is piezoelectric. Problems associated with LiNbO3~based integrated optics center around the needs to butt-couple a detector array to the waveguide, and the need to utilize other lens fabrication techniques. Significant progress has been made in recent years in devel­ oping high quality geodesic lenses and techniques to couple efficiently from the waveguide into a detector array. 9,10 These advances have led to the recent successful demonstration of working spectrum analyzers utilizing LiNb03 waveguides.11/ 12 Emphasis is now being placed on the optimization of the performance of the 10 SA and on the development of other integrated optical devices.Components for integrated optical spectrum analyzers in LiNbO3The development of the integrated optical spectrum analyzer on a LiNbO3 substrate re­ quired the fabrication of the following high quality components

Electroabsorption and electrorefraction properties of bulk and multiple quantum well structures made fr III-V compound semiconductor materials are discussed in this paper. The large electroabsorption that has already been observed is suitable for spatial light modulation. The potential advantages for using these structures for spatial light modulation include high speed of response and monolithic integration with detectors and electronic devices on the same chip. Variations of the electro-optical properties such as absorption wavelength birefringence. nonlinearity and speed of response as a function of structural© (1986) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A novel modulation technique is presented which facilitates the transmission of high frequency, fractional bandwidth signals in fibers. This approach uses the advantages of modelocked semiconductor lasers and external modulators. Narrow band (~ 10 GHz) modulation can be readily achieved at high center frequencies. Experimental realization of this concept is demonstrated with an acoustooptic modulation of modelocked optical pulses from a GaAs laser diode at a center frequency of 2.05 GHz and a bandwidth of 68.7 MHz.

The position of the focal plane, the intensity profile of the first diffraction spot and power losses have been measured for geodesic lenses in Ti-indiffused LiNb03 waveguides. It was intended for the focal plane of a geodesic lens to be situated at a waveguide edge; experimental results have shown that this was achieved to a tolerance of better than 12 im with two of the measured focal planes coinciding with the waveguide edge to within the +2 Inn accuracy of the measurement techniaue. Scans of the intensity profiles of focused diffraction spots have been made for one and two lens systems; the spot sizes in both cases were found to be

An externally modulated mode-locked laser diode is proposed to transmit high centre frequency, fractional bandwidth microwave signals over optical fibres. We demonstrate the feasibility of this scheme using an external Bragg cell to modulate (at 68.7 MHz) an actively mode-locked laser diode (mode-locked at 2.05GHz).

The effective propagation constants and electric field profiles of the propagating modes in dielectric channel waveguides are solved through a modification of the finite-element method called the product method. A tensor product of two one-dimensional spline spaces is used as the basis set for the two-dimensional electric field profiles. Schwartz distributions are used to treat discontinuities in the normal component of the electric field at discontinuities in the index profile. Comparisons of this method with analytically computed waveguide modes show that the product method is highly accurate: to more than six significant figures for the fundamental TE mode and to five significant figures for the fundamental TM mode.