In this paper, we have reviewed our recent works on IR supercontinuum generation (SCG) and its applications. First, we
provide a brief introduction on the motivations of the proposed effort. Second, the work of SCG in single crystal
sapphire fibers is reviewed. Third, in addition to single crystal sapphire fibers, the method, the process, and the results
of fabricating other IR waveguides are presented. Fourth, a quantitative simulation on the supercontinuum generation
with the new IR waveguide is provided, which shows that it is possible to generate SCG beyond 5 microns. To the best
knowledge of authors, this is the longest SCG reported so far. Finally, more experimental results of chemical analysis
with supercontinuum source are presented.
Because the efficiency of THz generation in air plasma is quite low, the residual power of input beam after THz
radiation is generated in air plasma remains almost the same. A new method, multiple air plasmas, is proposed. The
residual power can be used to induce other air plasmas and generate THz radiation again. The multiple air plasmas
method provides a potential way for the development of the intense THz source. The preliminary experimental
results confirm the theoretical prediction. The multiple air plasmas generated THz can be very useful for remote
THz generation and standoff detection.
In this paper, we experimentally verify that previously proposed idea of unequally spaced optical phased array can
greatly reduce grating-lobes. As the verification purpose of our previous numerical design, a laser beam is passed
through unequally-spaced slits, whose spacings are the same as the previous design. Interference patterns formed after
both 4- and 8-channel slits clearly show that the grating-lobes can be greatly minimized. To realize the beam steering
possible, optical waveguides array, which has unequally spaced design at the output ends is fabricated. The phase of
each beam can be varied using fibers array wound around PZT tubes before each beam is coupled into the waveguides
array. Interference patterns formed after the outputs of both 4- and 8-channel waveguides array show that the gratinglobes
can be greatly reduced using unequally spaced optical phased array technique.
In this paper, the two different mechanisms of supercontinuum generation in single crystal sapphire fibers according to
fiber lengths longer and shorter than dispersion length are theoretically and experimentally investigated. When the fiber
length is shorter than the dispersion length, self-phase modulation is the dominant factor for supercontinuum broadening.
A broad spectrum ranging from near-IR (1.2 μm) to the lower end of mid-IR (2.8 μm) is obtained. But, when the fiber
length is longer than dispersion length, soliton-related dynamics with self-phase modulation is the dominant factor for
supercontinuum. We further demonstrate that supercontinuum in a sapphire fiber can extend beyond the range of silica
fibers by showing the spectrum from 2 μm to 3.2 μm. Also, we successfully apply the supercontinuum source generated
from a sapphire fiber to IR spectroscopy. The spectra of pseudo-TNT chemical measured using our own supercontinuum
source is in good agreement with those obtained by FTIR. Supercontinuum generation using a sapphire fiber, which has
high damage threshold and broad transmission ranges can be used in many applications such as IR spectroscopy,
broadband LADAR, remote sensing, and multi-spectrum free space communications.
In this paper, we report the fabrication of higher-order-mode rejected fiber Bragg gratings (FBGs) in sapphire crystal fiber using infrared (IR) femtosecond laser illumination. The grating is tested in high temperature furnace up to 1600 degree Celsius. As sapphire fiber is only available as highly multimode fiber, a scheme to filter out higher order modes in favor for the fundamental mode is theoretically evaluated and experimentally demonstrated. The approach is to use an ultra thin sapphire crystal fiber (60 micron in diameter) to decrease the number of modes. The small diameter fiber also enables bending the fiber to certain radius which is carefully chosen to provide low loss for the fundamental mode LP01 and high loss for the other high-order modes. After bending, less-than-2-nm resonant peak bandwidth is achieved. The grating spectrum is improved, and higher resolution sensing measurement can be achieved. This mode filtering method is very easy to implement. Furthermore, the sapphire fiber is sealed with hi-purity alumina ceramic cement inside a flexible high temperature titanium tube, and the highly flexible titanium tube offers a robust packaging to sapphire fiber.
Our high temperature sapphire grating sensor is very promising in extremely high temperature sensing application.
Novel supercontinuum generation by launching ultra-short femtosecond laser pulses into single crystal sapphire fibers is
demonstrated. Supercontinuum generation using sapphire fiber exhibits many advantages that include high transparency
up to 5 micron, low material dispersion in the 0.8 micron to 5 micron spectral range, and an extremely high laser damage
threshold (500 times higher than that of silica). Thus, supercontinuum spectrum with high power, super broadband, and
spatial coherence can be realized by pumping single crystal sapphire fibers. By experimental comparison, we prove that
sapphire fiber can provide a broader supercontinuum spectrum than that of bulk sapphire counterpart under the same
exciting conditions. Since supercontinuum generation in single crystal sapphire fibers can radiate high power
supercontinuum in the middle-IR regime, it will have a great impact on many applications, including sensing and
broadband multi-spectrum free space communications.
We demonstrate a broad supercontinuum source by bridging two separate supercontinua that are pumped at two different
IR wavelengths. Two separate supercontinua are overlapped to form a broadband supercontinuum source without
spectrum discontinuity between two different pumping sources. The bridging effect of two separate supercontinua is
successfully demonstrated by applying two pumping sources at 1460 nm and 1769 nm into a regular single mode fiber.
Also, more than 1000 nm expansion possibility due to the bridging effect can be achieved by pumping at 1350 nm and
1963 nm.
By using only two input signals of A and B, an all-optical half adder that utilizes a cross gain modulation in
semiconductor optical amplifiers is demonstrated at 10 Gbps. The half adder utilizes two logic functions of SUM
and CARRY, which can be demonstrated by using the XOR gate and the AND gate, respectively. The extinction
ratios of SUM and CARRY are approximately 6.1 dB. No additional input beam such as clock signal or
continuous wave light, which is required in many other all-optical logic gates, is used in this design concept.
In this paper, we will present our preliminary results on our development of infrared and terahertz generation by ultrafast laser pulses. The objective of this project is to develop (i) portable and cost effective spatially coherent broadband Infrared (IR) and Terahertz (THz) illuminating light sources. To effectively generate spatially coherent broadband IR and THz sources, we use a novel nonlinear optical technical approach by harnessing the huge nonlinear effect of the specially designed and fabricated photonic crystal fibers (PCF). The major merits of these unique light sources are: (1) broad band (covering a wide range of spectroscopic signatures), (2) spatially coherent (so that beams can be delivered to the far distance like laser beams), (3) compact, portable and small footprint (all fiber design), (4) cost effective (traditional approaches such as cascaded laser systems are complicated and expensive for covering broadband).
In this paper, we theoretically and experimentally demonstrate that the major drawbacks of current beam scanning
systems can be drastically reduced. First, the scanning speed of several MHz level has been achieved using an optical
phased array. Since the increased scanning speed causes the lower scanning resolution due to the less number of pulses
per pixel, multiplexing techniques to increase the repetition rate of a beam scanner have been demonstrated. The fiber
multiplexing techniques have been demonstrated in serial and parallel configurations, which can be selected for different
requirements and applications.
In this paper, we review currently available fiber-optic gyroscope (FOG) technologies and major noise factors limiting
the performance of FOGs. We investigate possible solutions to noise factors including Rayleigh backscattering, Kerr
effect, Faraday, and Shupe effects. Based on these solutions, we present the possible design of an interferometric FOGs
employing microstructured fibers. A supercontinuum source can minimize Rayleigh backscattering and Kerr effect by
reducing the coherence length of FOGs. Also, by using a photonic bandgap fiber with hollow core, Kerr, Faraday and
Shupe effects can be minimized.
KEYWORDS: Logic, Semiconductor optical amplifiers, Modulation, Logic devices, Clocks, Electrons, Signal processing, Optical signal processing, Signal generators, Computing systems
By using cross gain modulation in semiconductor optical amplifiers, basic logics for all-optical computing
and signal processing are successfully demonstrated at 10Gbps. These functions will bring up the increased
speed and capacity of telecommunication systems, basic or complex optical computing, and many other optical
signal processing systems.
In this paper, we present a low grating lobe optical beam steering technique using unequally spaced phased array, in which the required spacings among phase elements are quantitatively analyzed so that the grating lobe can be minimized by the destructive interference from these unequally spaced phase elements. The large grating lobe is one of the major drawbacks of optical phased array technology, which limits the light efficiency and quality of the light beam. Thus, the low grating lobe technique presented in this paper could substantially improve the light efficiency and the quality of light beam, which may play an important role in a variety of applications such as fast speed ladar beam steering, large size high resolution display, and wide bandwidth free space optics communications.
An all-optical full adder using semiconductor optical amplifiers has been demonstrated at 10 Gbps for the first time. The full adder consisted of XOR and NOR gates only utilizes the mechanism of cross-gain modulation. The full adder utilize two logic functions of SUM and CARRY, which can be demonstrated by using two XOR gates and four NOR gates, respectively. By passing signal A as probe signal and signal B as pump signal into SOA-1, Boolean A NOT B can be obtained. Also, by changing the role of signals A and B for SOA-2, Boolean NOT A B can be acquired. Addition of Boolean A NOT B and NOT A B results in NOT A B + A NOT B , which is Boolean expression of logic XOR. By passing this XOR signal and signal C into the second XOR gate with the same principle, SUM signal of the full adder can be obtained. The Boolean expression of SUM can be expressed as A # B # C . With the first three NOR gates, Boolean NOT(A+B), NOT(B+C), and NOT(C+A) can be obtained. With the addition of these outputs, Boolean NOT(A+B) + NOT(B+C) + NOT(C+A) can be formed. By injecting these outputs through the last NOR gate with clock signal, CARRY signal of the full adder can be realized. The Boolean expression of CARRY can be expressed as AB +BC +CA. The extinction ratio is about 6.1dB.
By using gain nonlinearity characteristics of semiconductor optical amplifier, an all-optical binary half adder at 10 Gbps is demonstrated. The half adder operates in single mechanism, which is XGM. The half adder utilizes two logic functions of SUM and CARRY, which can be demonstrated by using the XOR gate and the AND gate, respectively. In the XOR (A NOT B + NOT A B) gate, Boolean A NOT B is obtained by using signal A as a probe beam and signal B as a pump beam in SOA-1. Also, Boolean NOT A B is obtained by using signal B as a probe beam and signal A as a pump beam in SOA-2. By adding two outputs from SOA-1 and SOA-2, Boolean A NOT B + NOT A B (logic XOR) can be obtained. In the AND (AB ) gate, Boolean NOT B is firstly obtained by using signal B as a pump beam and clock signal as a probe beam in SOA-3. By passing signal A as a probe beam and NOT B as a pump beam through SOA-4, Boolean AB is acquired. By achieving this experiment, we also explored the possibilities for the enhanced complex logic operation and higher chances for multiple logic integration.
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