We fabricated a fiber laser that uses a thin semiconductor layer surrounding the glass core as the gain medium. This is a completely new type of laser. The In2Te3 semiconductor layer is about 15-nm thick. The fiber laser has a core diameter of 14.2 μm, an outside diameter of 126 μm, and it is 25-mm long. The laser mirrors consist of a thick vacuum-deposited aluminum layer at one end and a thin semitransparent aluminum layer deposited at the other end of the fiber. The laser is pumped from the side with either light from a halogen tungsten incandescent lamp or a blue light emitting diode flash light. Both the In2Te3 gain medium and the aluminum mirrors have a wide bandwidth. Therefore, the output spectrum consists of a pedestal from a wavelength of about 454 to 623 nm with several peaks. There is a main peak at 545 nm. The main peak has an amplitude of 16.5 dB above the noise level of −73 dB.
A true three dimensional camera is described here, that without using
the stereoscopic effect can measure the distance from each pixel to the point
on the object that is in focus at the pixel. It is useful for providing detailed
range information for guiding autonomous vehicles and general robotic
vision.
It is conventionally assumed that humans have three dimensional vision because each
object is observed from a slightly different direction with each eye. That is, humans have
stereoscopic vision. This is true. However, there is another mechanism in animal eyes that
also contributes to three dimensional vision. The Depth Perception Camera described here
also uses this mechanism.
The Depth Perception Camera can be be constructed by conventional semiconductor
device fabrication technology. It can also be constructed using a three dimensioal printer that
can handle differently doped semiconductors.
An imager that can measure the distance from each pixel to the point on the object that is in focus at the pixel is described. Since it provides numeric information of the distance from the camera to all points in its field of view it is ideally suited for autonomous vehicle navigation and robotic vision. This eliminates the LIDAR conventionally used for range measurements. The light arriving at a pixel through a convex lens adds constructively only if it comes from the object point in focus at this pixel. The light from all other object points cancels. Thus, the lens selects the point on the object who's range is to be determined. The range measurement is accomplished by short light guides at each pixel. The light guides contain a p - n junction and a pair of contacts along its length. They, too, contain light sensing elements along the length. The device uses ambient light that is only coherent in spherical shell shaped light packets of thickness of one coherence length. Each of the frequency components of the broad band light arriving at a pixel has a phase proportional to the distance from an object point to its image pixel.
An imager that can measure the distance from each pixel to the point on the object that is in focus at the pixel is described. This is accomplished by short photo-conducting lightguides at each pixel. In the eye the rods and cones are the fiber-like lightguides. The device uses ambient light that is only coherent in spherical shell-shaped light packets of thickness of one coherence length. Modern semiconductor technology permits the construction of lightguides shorter than a coherence length of ambient light. Each of the frequency components of the broad band light arriving at a pixel has a phase proportional to the distance from an object point to its image pixel. Light frequency components in the packet arriving at a pixel through a convex lens add constructively only if the light comes from the object point in focus at this pixel. The light in packets from all other object points cancels. Thus the pixel receives light from one object point only. The lightguide has contacts along its length. The lightguide charge carriers are generated by the light patterns. These light patterns, and thus the photocurrent, shift in response to the phase of the input signal. Thus, the photocurrent is a function of the distance from the pixel to its object point. Applications include autonomous vehicle navigation and robotic vision. Another application is a crude teleportation system consisting of a camera and a three-dimensional printer at a remote location.
An imager that can measure the distance from each pixel to the point on the object that is in focus at the pixel is
described. This is accomplished by a short photoconducting lossi lightguide section at each pixel. The eye or
camera lens selects the object point who’s range is to be determined at the pixel. Light arriving at an image point
trough a convex lens adds constructively only if it comes from the object point that is in focus at this pixel.. Light
waves from all other object points cancel. Thus the lightguide at this pixel receives light from one object point
only. This light signal has a phase component proportional to the range. The light intensity modes and thus the
photocurrent in the lightguides shift in response to the phase of the incoming light. Contacts along the length of
the lightguide collect the photocurrent signal containing the range information. Applications of this camera
include autonomous vehicle navigation and robotic vision. An interesting application is as part of a crude
teleportation system consisting of this camera and a three dimensional printer at a remote location.
We have fabricated and tested Gold Cylinder Fiber (GCF) bio sensors. The sensor fiber
has a thin, approximately 3 nm to 5 nm thick, Gold alloy film layer at the glass core glass
cladding boundary. One end of the fiber is etched to let the gold alloy cylinder protrude
about 10 m. A Single Mode Fiber (SMF) is connected to the other end of the GCF. Light
propagates through the SMF to a short section of GCF. The etched end of the GCF is
dipped into the fluid to be analyzed. The reflected light from the sample returns back
through the SMF to a spectrum analyzer.
We fabricate optical fiber with the same dimensions as standard communication single mode fiber (SMF) with the
glass core surrounded by 40 to 60 nm thick lithium niobate (LiNbO3) film as schematically shown in Fig 1. Lithium
Niobate Cylinder Fiber (LNCF) can be used as strain sensor and sonar detector. We use the LNCF in a mode where
the strain causes a change in the light propagating through the fiber.
It is possible that each light sensor pixel in the eye has the capability of measuring the distance to the part of the object in focus at the pixel. One can also construct an electronic camera where each pixel can measure the distance to the portion of the object in focus at the pixel. That is, these devices have depth perception
We have developed optical fibers with a thin approximately 40 to 60 nm thick Lithium Niobate Layer
at the glass core and cladding boundary. These Lithium Niobate Cylinder Fibers (LNCF) are now in the
process of being commercialized as strain gauges for bridges, tunnels, pipe lines and aircraft components.
An application as a sonar sensor is also being investigated. LNCF strain sensors use light amplitude
detection rather than phase detection. Amplitude detection is easier to implement and is substantially less
costly. LNCF's when used as light amplitude sensing sonar detectors are over 1000 times more sensitive
than standard Single Mode Fibers. LNCFs use so called "Non Propagating" light modes rather than the
conventional propagating modes.
We are in the process of developing a hollow core fiber that contains a 2 nm to 3 nm thick AlAu alloy film near the core region, see Fig. 1. The fiber has a Photonic Crystal cladding that reflects the light back into the core region.
The authors analyze electromagnetic wave propagation through optical fibers consisting of a glass core surrounded by a high-refractive-index dielectric thin film, in turn surrounded by a glass cladding. The asymmetry of the structure due to different core and cladding refractive indices results in two types of guided modes: they propagate either in the core and film or only in the film. The dispersion equations are derived, and mode classifications are established for transverse and hybrid modes. The cutoff conditions of transverse modes are given. Numerical simulations are performed to obtain the effects of film index and thickness on the cutoff frequencies and dispersion curves. It is shown that a high-index film causes the modes to become evanescent in the core and guided only in the film. These modes form two types of linearly polarized modes, according as they follow the TE or the TM mode propagation curves of asymmetric slab waveguide. Investigation of power flow along the propagation direction shows that the higher the refractive index of the film, the higher the power density in the film.
We have developed optical fibers with a very thin Lithium Niobate Layer at the glass core
glass cladding boundary it is observed that the Lithium Niobate Cylinder Fibers have a
large strain induced light loss of about 2.12784 x 10-5 per kg per m. These fiber can be
used as strain sensors operating in an amplitude mode rather than in the phase detection
mode as is the case for strain sensors using standard Single Mode Fibers.
Light propagation through optical fibers consisting of a glass core coated with a high refractive index uniaxial dielectric thin film, in turn surrounded by a glass cladding, is presented. The dispersion equations are derived, and mode classifications are established for transverse and hybrid modes. Simulation results of lithium niobate thin film with bulk material dispersion are given as an example of uniaxial film. It is shown that modes are guided mainly in the film and the structure is capable of strong light confinement. Investigation of power flow along the propagation direction shows that the higher the film thickness, the higher the power density in the film.
Light absorption spectrum measurements and the light intensity dependence of the light absorption spectrum of a fiber with a very thin gold film at the glass core glass cladding boundary are presented. The thickness of the gold film is less than the scattering length of electrons in this metal. The absorption spectrum appears to be strongly light intensity dependent. We also observed the mode structure of light propagating through the gold film. Our fabrication process can produce large area very thin metal films that are very difficult to produce by other methods.
A MOEMS fiber modulator/sensor is fabricated by depositing a lithium niobate sol-gel thin film between the core and cladding of a fiber preform. The preform is then drawn into 125-µm fibers. Such a MOEMS modulator design is expected to enhance existing lithium niobate undersea acousto-optic sound wave detectors. In our proposed version, the lithium niobate thin film alters the ordinary silica core/cladding boundary conditions such that, when a stress or strain is applied to the fiber, the core light confinement factor changes, leading to modulation of fiber light transmission. Test results of the lithium niobate embedded fiber with a 1550-nm, 4-mW laser source revealed a reduction in light transmission with applied tension. As a comparison, using the same laser source, an ordinary silica core/cladding fiber did not exhibit any reduction in transmitted light when the same strain was applied. Further experimental work and theoretical analysis is ongoing.
A theoretical analysis of the light absorption and gain mechanisms in a Cd3P2 Semiconductor Cylinder Fiber is presented. The results of these calculations are in good agreement with previously published experimental data. Cd3P2 has two direct energy gaps, which both influence the gain mechanism. Pump light can be used to reduce the absorption. Stronger pump light that generates more charge carriers will produce net gain (gain above absorption compensation). The fiber exhibits gain over a very wide light wavelength bandwidth.
We have measured a net gain of 19.5 dB in a 4 mm long piece of Cd3P2Semiconductor Cylinder Fiber (SCF) at a wavelength of 1550 nm. The fiber was pumped from the side with a 100 mW, 832 nm laser. Side pumping is very inefficient since only a small portion of the pump light is absorbed by the very thin, approximately 6.694 nm thick, semiconductor film. However, this pumping arrangement is very convenient and does not require wavelength sensitive input and output couplers. We also measured the absorption spectrum. The absorption spectrum is in good agreement with a theoretical model. The absorption spectrum exhibits a step due to the two direct energy gap conduction bands of the Cd3P2 semiconductor film.
An fiber modulator/sensor has been fabricated by depositing a lithium niobate sol-gel thin film between the core and cladding of a fiber preform. The preform is then drawn into 125 um fiber. The proposed design of lithium niobate cylinder fibers can enhance the existing methdology for detecting sound waves under water utilizing the acoustooptic properties of lithium niobate. Upon application of a stress or strain, light propagating inside the core, acording to the principle of total internal reflection, escapes into the cladding because of the photoelastic boundary layer of lithium niobate. Test results of the lithium niobate fiber reveal a reduction in the 1550 nm, 4 mW source with applied tension. The source power from an ordinary quartz fiber under the same stress condition remained invariant to applied tension.
We have fabricated fibers with an a few nm thick Cd3P2 semiconductor layer at the clear glass core glass cladding boundary. We have measured a gain of approximately 7.1 dB in a 4 mm long piece of this Semiconductor Cylinder Fiber (SCF) at a wavelength of 1550 nm. The fiber section was pumped from the side with a 38 mW laser operating at a wavelength of 980 nm. We have reason to believe that the test wavelength of 1550 nm is near the short wavelength end of about a few hundred nm wide gain curve. The SCFs have applications as broad band Fiber Light Amplifiers.
We are currently working on Semiconductor Cylinder Fibers (SCF), fibers with a thin semiconductor layer at the glass core glass cladding boundary. We hope that these fibers can eventually be used as both S aturable Absorbers (SA) and Fiber Light Amplifiers (FLA). We use a rod and tube method for fabricating these fibers. The three fabrication process steps, semiconductor deposition, collapse, and fiber drawing have been working well since the summer of 1 999. We have mathematical models for the fabrication process steps that allows us to calculate the required temperatures and pressures used. The fabrication process is very reproducible.
Tapped delay line is a fundamental building block for designing filters and signal processors, specially the adaptive ones. For an example, true time-delay lines are indispensable for electronically beam steered phased array antenna system with multiple nulling capability. Photonic implementation of the delay line with wide bandwidth approaching 100 GHz uses either variable length or variable group velocity as a function of wavelength. Fiber Bragg reflection grating plays an important role for the first case whereas highly dispersive fiber/waveguide or material are the ingredients for the second case. High dispersion is obtained near a resonance of the transmission or absorption curve of the fiber. The resonance properties can be enhanced by using nanoparticles with complex structures such as metal coated dielectric spheres or using so-called photonic bandgap materials. This paper reviews the status of photonic implementation of the delay lines using Bragg gratings, high dispersion fibers, bandgap engineered materials, among others. Theoretical and experimental results are presented for a high dispersion fiber achieved by resonances in a thin metallic film surrounding the fiber core.
We have fabricated and tested fibers having a thin AlCu alloy film strip covering a 15 degree of arc along the core cladding boundary. The fabrication of these fibers had a dual purpose. In order for the metal film to deform smoothly during the fiber pulling process from a coating on the 1 mm diameter core rod in the preform to a coating of the 10 micrometer core in the fiber the viscosity of the metal must be less than the viscosity of the surrounding glass. The viscosity of the AlCu film can be conveniently changed by varying the composition of the alloy. These fibers can, eventually, be used as polarizers. Light polarized parallel to the metal strip is absorbed more than light polarized perpendicular to the strip. We tested both the spectral and polarization transmission properties of these fibers.
We successfully placed a metal strip along the core of an optical fiber, see Fig. 1. These devices can be used as polarizers. Light polarized parallel to the metal strip is absorbed while light polarized perpendicular to the metal strip is absorbed less. Potentially large ratios of transmitted to absorbed light can be achieved in relatively short pieces of fiber. The Metal Strip Polarizing Fibers (MSPFs) are typically about 5 mm long. We report both on the fabrication process and some preliminary test.
We have fabricated and tested coupled integrated coupled and branching waveguide lasers in Nd glass substrates1 . By making two or more parallel diffused channel or ridge waveguides close together on rare-earth doped glass substrates as shown in Fig's 1 , a set of coupled waveguide lasers can be fabricated which produce two closely spaced light waves, the symmetric and anti symmetric modes of the structure. The difference between their frequencies is in the microwave regime. Such devices can serve as single-sideband optical carrier sources. We have fabricated both diffused channel waveguides as shown in Fig. 1 a and ridge waveguides as shown in Fig. lb. The ridge waveguides can be bend through smaller radii than diffused wave guides for the same loss of light.
One of the major problems with both Semiconductor Cylinder Fibers (SCF) and semiconductor Micro Crystals
(MC) in glass is surface states at the semiconductor glass interface. We here make a model for the surface states,
analyze their effect and the effect ofbarrier layers.
Both, the fact that no shift in energy due to a quantum size effect is observed in the SCF and that the recombination
of optically excited charge carriers seems to be by non radiative processes is, probably, due to surface states at
the semiconductor glass interfaces. In order to investigate the effect of surface states we model the surface states
Fibers containing nonlinear optical material have large interaction length. Therefor it is possible to use small amounts of nonlinear material in the fiber and obtain large nonlinear effects. One of the easiest methods of placing a nonlinear material into a fiber is to surround the core of the fiber with a thin cylinder of nonlinear optical materials. We investigate such a fiber in this paper.
The switching response of a CdTe-InSb nonlinear etalon subject to an intense light beam is reported. The device is illuminated with a high intensity pulsed pump beam and a low intensity pulsed probe beam. The pump beam has a wavelength that corresponds to a negative slope of the low intensity reflectance spectrum of the etalon and has sufficient power to change the index of refraction in the etalon cavity. This causes a shift of the spectrum, a decrease in the reflectivity, and an increase in the electric field in the etalon cavity which further shifts the spectrum. This process continues until a minimum reflection level is reached. The output yields the convolution of the probe beam with the device response to the pump pulse. It appears that the switching response of the etalon is much faster than could be determined with the 100 ps pulses used.
The Artificial Long Delay Optical Processor (ALDOP) generates a large variable delay of a band limited pulse modulated RF signal. The proposed prototype ALDOP has potential use in a Passive Radio Ranging (PRR) system operating in the 82.5 - 97.5 MHz frequency band. The complete system will combine a passive electronic band pass filter with the optically based ALDOP to impart a unique phase shift to each frequency component of an incoming RF signal. The phase shift is generated using optical heterodyne methods that incorporate the transmission and modulation of light through a series of optical components including an acousto-optical cell and a Fresnel Zone Plate.
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