This work investigates the radio-frequency (RF) linewidth characteristics of a single-section quantum dot self-mode-locked laser under a self-injection locking configuration to achieve a stable and compact on-chip pulsed light source. The results indicate an absence of chaotic oscillation and longitudinal mode broadening under the strongest optical feedback conditions. The quantum dot laser exhibits high tolerance to optical feedback, with significant RF linewidth compression, resulting in stable pulse generation. These findings suggest that singlesection quantum dot lasers are promising candidates for on-chip integrated pulsed light sources, offering new opportunities for applications in spectroscopy and quantum optics.
We propose a hardware-efficient, low-cost integrated communication and vibration sensing method that relies solely on existing commercial coherent optical communication systems. The scheme utilizes dynamic frequency offset estimation to adapt to commercial 100kHz ECL, while employing sliding averaging and nearest-neighbor interpolation to greatly reduce algorithm complexity, making it conducive for integration into real-time platform. We demonstrate our scheme in a dual-polarization DSCM coherent optical communication system and discuss the performance in terms of communication and sensing capabilities under different conditions.
KEYWORDS: Sensors, Temperature metrology, Temperature sensors, Ring lasers, Polydimethylsiloxane, Fiber lasers, Interferometers, Signal to noise ratio, Single mode fibers, Photonic crystal fibers
A mode interferometer coated with polydimethylsiloxane (PDMS) film based on photonic crystal fiber (PCF) is embedded into the fiber ring laser (FRL) sensing system for temperature and relative humidity measurement. High optical signal to noise ratio (OSNR) of ~54 dB, narrow 3 dB bandwidth of ~0.26 nm, and high-quality factor Q of 6×103 were obtained, which indicate that the designed FRL system has ability to realize the measurement of environmental parameters with high resolution and accuracy and has potential application in remote monitoring of temperature. As the temperature increased from 35 °C to 115 °C, the spectral response has wavelength blue-shifts trend. The average temperature sensitivity of temperature sensor based on PCF is 90 pm/°C with small error bar and excellent linear correlation coefficient of 0.992. The average temperature sensitivity of temperature sensor based on PCF is 89 pm/℃ during the cooling process, revealing the proposed sensor has excellent reversibility. In addition, the sensor is insensitive to the change of relative humidity. Furthermore, the stability of temperature sensor based on PCF was experimentally demonstrated and analyzed. The maximal dip wavelength shifts of the peaks at 45 °C and 95 °C were 0.074 and 0.075 nm, respectively, within 3 hours. Besides, the FRL temperature sensor based on PCF has simple structure, excellent reversibility, repeatability, and stability. Therefore, the proposed FRL temperature sensor based on PCF has a great potential in practical applications where the high measurement precision and accuracy is required such as chemical reaction.
A multi-beam interference theory called internal-external cavity Vernier effect in cascaded Fabry–Pérot interferometer (FPI) was proposed and analyzed. Through that theory, simultaneous measurement of relative humidity (RH) and temperature could be achieved. The cascaded FPI consists of an air cavity and a chitosan cavity. The envelope of the spectrum of the proposed sensor can restore the information of the chitosan cavity, and the high frequency fringe is the sum of the information of the two cavities. By tracing the wavelength shifts of the envelope and high-frequency fringes, a sensitivity coefficient (SC) matrix of the relatively humidity (RH) and temperature could be obtained. The experimental RH sensitivities for the envelope and high-frequency fringe were 1.599 nm/%RH and 0.071 nm/%RH, respectively. Temperature sensitivities of -0.045 nm/℃and 0.035/℃ were obtained for the envelope and high-frequency fringe, respectively. The crosstalk between the RH and temperature was eliminated by the SC. This Vernier effect provides a dual-parameter measurement function and explains the multi-beam interference in cascaded FPI.
Exceptional points (EPs) in whispering-gallery-mode microresonators systems have attracted substantial attention due to their intriguing and anomalous optical characteristics. Recently, EPs have been experimentally observed in silicon microrings with coupling manipulation elements, such as an S-shaped waveguide and notch. In this paper, the observation of EP in a nanocylinder-loaded silicon microring is experimentally demonstrated. The device consists of a 5- μm microring with two nanocylinders placed close to the outer edge of the microring. By tailoring the size and position of the two nanocylinders, the fully asymmetric coupling between the clockwise- and counterclockwise-propagating modes occurs, leading to the implementation of EP. Experimentally, the spectral response is investigated by single-side excitation from clockwise and counter-clockwise directions. The reciprocal transmission and nonreciprocal reflection spectra are observed, which confirms the proposed device works in the vicinity of EP. The construction of EP in silicon microring paves the way to basic science and applied technology in non-Hermitian physics.
We experimentally demonstrate that InAs/GaAs quantum dot (QD) lasers exhibit high reflection insensitivity in the wide temperature range of 293 K to 353 K, which is due to the low and thermal stable linewidth enhancement factor. This work shows the potential of QD lasers as uncooled and isolator-free on-chip laser sources for next-generation photonic integrated circuits.
In this paper, a dual-wavelength square pulses fiber laser with tunable pulse width based on nonlinear polarization rotation and nonlinear effect was studied. The fiber laser containing a 1050-m highly nonlinear fiber operated at central wavelengths of 1533 nm and 1569 nm and the repetition rate was 194.7 kHz. While the polarization state of the laser was unchanged, the pump power was increased from 100 mW to 300 mW, and the pulse width was extended from 163.6 ns to 558.2 ns. In this process, the maximum energy of a single pulse was 8.57 nJ. The simple, compact square pulse dual wavelength fiber laser with tunable pulse width can meet great potential for applications.
We propose to leverage a silicon-organic hybrid integration structure to implement an integrated entangled photon pair source with high photon pair generation rate. This method combines the weak nonlinear absorption of organic materials with the high light confinement of silicon waveguides. Due to the supression of TPA and FCA, the pump power saturation threshold of the hybrid waveguide can be greatly increased. Therefore, with the high nonlinear coefficient and strong pump power, this hybrid integrated structure can achieve high photon pair generation rate. This work shows that silicon-organic hybrid integration could be a competitive platfrom for quantum photonic circuits.
We demonstrated a large aperture 1×16 silicon photonics OPA leveraging one-millimeter-long subwavelength grating antennas (SGA). The SGA is implemented by placing subwavelength silicon segments in the vicinity of the conventional strip waveguide so that they only interact with the evanescent field of the strip waveguide. The strength of the SGA can be conveniently controlled by tuning the location and size of the silicon segments. With the 1×16 OPA, a light beam of 0.1°×1.8° with a sidelobe suppression ratio > 10 dB is achieved.
We demonstrate an EP-based sensor based on exceptional point(EP) of nanocylinders-loaded silicon microring for single particle detection. The EP is implemented by tailoring the spatial phase difference between the two nanocylinders placed close to the microring. When a nanoparticle is adsorbed onto the surface of the silicon microring, the degeneracy of two eigenvectors of the silicon microring is lifted, leading to mode splitting in the transmission spectrum. The wavelength difference of the split-mode is proportional to the square-root of the perturbation. To the best of our knowledge, this is the first sensor leveraging the EP of a silicon microring for single nanoparticle detection
Silicon photonics optical phased arrays have been studied intensively in recent years. As the divergence angle of the light beam is inversely proportional to the size of optical antennas, developing long grating emitters is crucial to the implementation of large aperture optical phased arrays. However, because of the high refractive index contrast between silicon and cladding materials on silicon-on-insulator (SOI) platform and fabrication limitation, the grating strength of a conventional grating is so strong that the light can only propagate a short distance within the grating. Because of the capability to engineer the macro optical properties of materials, subwavelength structures have become important building blocks in integrated photonics. In this paper, we propose subwavelength silicon segments as a promising approach to form long grating emitters. Subwavelength segments are placed a distanced away from a conventional waveguide to assure that they only interact with the evanescent wave of the guided mode. The grating strength can be tailored to any values of interest by optimizing the dimensions and positions of subwavelength segments. As a proof-ofconcept, a millimeter-long, through-etched grating and an apodized grating are designed and fabricated, which shows a divergence angle of 0.081 ° and 0.079°.
Circular polarization shift-keying (CPolSK) modulation maps binary digital signals to the two circular polarization states of the optical carrier, which can be applied to the modulation-demodulation of free space optical communication systems. This paper constructs a new optical communication system that uses vortex beams with different orbital angular momentum (OAM) modes as the optical carriers to multiplex CPolSK modulated signals. And with limited OAM modes, we combine amplitude shift-keying (ASK) modulation and CPolSK modulation to construct a modulation and demodulation system which is similar to quadrature amplitude modulation. In the receiver, a designed reference beam is used to interfere with the signal beam. Then the hybrid modulation signals can be easily converted into the intensity changes that can be directly detected for demodulation. The numerical simulation results show that this modulation system can effectively expand the communication capacity of CPolSK modulation system. And after combining ASK and CPolSK, the system can get better communication performance. It shows a wide prospect in the field of free space optical communication.
A femtosecond mode-lock all-fiber laser based on the nonlinear multimode interference (NL-MMI) effect is demonstrated. The saturable absorber (SA) in this laser is a graded-index multimode fiber-step index multimode fibergraded-index multimode fiber (GIMF-SIMF-GIMF) structure. The laser can work in mode-lock or soliton mode-lock two states. Through finely turning the polarization controller (PC), the laser will change the operation state. When the laser is running in the mode-locked state, the pump threshold is 51.4 mW. The center wavelength of the mode-lock pulse is 1559.71 nm with a spectral bandwidth of 10.73 nm, 354 fs duration and the fundamental repetition rate of 10.8 MHz. When the laser working in the soliton mode-lock state, the pump threshold is 54.1 mW. The center wavelength of the soliton pulse is 1561.85 nm, and the spectral bandwidth is 4.01 nm. The lasers have environmental stability. After a slight disturbance, the laser can stabilize itself to the mode-locked state.
We demonstrated an experimental observation of bright-dark pulse pair and soliton bunch in mode-locked erbium-doped fiber ring laser with the saturable absorber (SA) of graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF), which utilizes nonlinear multimode interference inside the multimode fiber to realizing mode locking of fiber laser. During the experiment, we observed a fascinating phenomenon of dualwavelength bright-dark pulse pair, in which the wavelengths of the two wavelengths are 1558.5 nm and 1560.1 nm, respectively, and the wavelength interval is 1.6 nm. The PBS filter was used to verify that the bright and dark pulses are orthogonal to each other in polarization. We also obtained multiple set of soliton bunches running at the fundamental frequencies of 100.5 ns, and when we increase the pump power we could find that the number of optical solitons increases in a single soliton bunch, which experimental phenomenon is in appropriate agreement with the theory. Based on the observation and understanding of these experimental phenomena, it is beneficial to explore the rich nonlinear effects in the mode-locked fiber laser.
A joint blind equalization algorithm is proposed for compensating polarization-dependent loss (PDL) and random state-of-polarization (RSOP) rotation in a Stokes vector direct detection (SV-DD) system based on a time domain extended Kalman filter (EKF) algorithm. The numerical results confirm that the algorithm has a good performance which can track fast random SOP rotation up to 1.5Mrad/s even when 3dB PDL before and after fiber link is present for high-order modulation format.
We investigate the conversion of mode locking of bright pulses, dark pulses and dark-bright pulses in an Erbium-doped fiber laser (EDFL) based on a Molybdenum disulfide (MoS2) films saturable absorber (SA) experimentally. When the pump power is 150 mW, by changing the polarization controller (PC) to change the polarization state in the laser cavity, we observed the bright pulse trains, the dark pulse trains and the dark-bright pulses trains in turn. All pulse interval are about 58 ns, and the repetition frequency of pulse is 1.7 MHz. The study provides a method for the conversion among bright pulses, dark pulses and dark-bright pulses.
Ultrasonic nondestructive testing plays a more and more important role in modern production and construction. In this paper, a novel ultrasonic energy transfer technique based on peanut shape structure is proposed and demonstrated. The ultrasonic device is able to effectively couple the laser energy in the fiber core to the cladding of the single-mode fiber (SMF) by using the micro machined fiber structure. The laser energy coupled to the cladding can be absorbed by the ultrasonic conversion material coated on the surface of the SMF. Due to the ultrasonic conversion material has high thermal elastic coefficient, it can produce mechanical expansion and contraction process after absorbing the laser, resulting in the generation of the ultrasonic signal. The ultrasonic transducer based on peanut shape taper only needs to be fused by SMF and fiber splicer. The proposed laser-ultrasonic transducer has many advantages, such as simple preparation, cost-effective, and high energy conversion efficiency. Such characteristics makes the proposed laser-ultrasonic transducer attractive for practical applications.
An all-fiber Fabry-Perot interferometer (FPI) strain sensor based on offset splicing fibers and Vernier effect is proposed and experimentally demonstrated. The proposed sensor consists of two separated air-cavity FPIs connected by a long section of single mode fiber (SMF) in a fiber link. The two separated FPIs have approximately equal optical paths, so that the Vernier effect can be generated. One FPI is used as the sensing FPI (SFPI) for strain measurement, which is formed by splicing a section of microfiber between two SMFs with large lateral offset. The other FPI is used as the reference FPI (RFPI) to employ the Vernier effect and amplify the sensitivity, which is formed by splicing a section of silica tube between two SMFs. Compared to a single FPI based sensor, the strain sensitivity of the proposed sensor with Vernier effect can be improved by tens of times. The strain sensitivity of our proposed sensor reaches 1.3 nm/με, which is the highest strain sensitivity of fiber sensor based on FPI and wavelength demodulation mechanism. Since the aircavity SFPI is insensitive to temperature, the proposed sensor also exhibits low temperature sensitivity of 50.2 pm/℃. With the advantages of high strain sensitivity, low temperature cross-sensitivity, compact size and easy fabrication, the proposed sensor has great applications in many fields.
A joint compensation scheme for IQ imbalance and phase noise based on the extended Kalman filter is proposed. Our proposed scheme can compensate IQ imbalance and the phase noise jointly with quick convergence speed and excellent BER performance.
We demonstrate the first 60 W Tm3+-doped all-fiber laser with single-mode 10/130 fiber and compact air-cooling thermal management way at 1945 nm. The overall optical conversion efficiency reaches 42.2%. High laser power stability of <1.5% is obtained during a continuous test time of >15 hours. The spectra linewidth at maximum output is evaluated as only 0.19 nm. Meanwhile, its direct bonding applications on kinds of transparent plastics are presented.
KEYWORDS: Polarization, Filtering (signal processing), Signal to noise ratio, Tolerancing, Digital signal processing, Adaptive optics, Interference (communication), Signal detection, Optical engineering, Detection and tracking algorithms
An adaptive Kalman filter (AKF) scheme for joint polarization and phase recovery is proposed and experimentally demonstrated. In this scheme, the noise covariance is estimated adaptively along with the recursive of KF. The simulation results show that the tuning parameter Q can adaptively converge to an optimal value in wide ranges of optical signal-to-noise ratio (OSNR), polarization rotation frequency, and laser linewidth. As a result, the proposed AKF has less OSNR sensitivity penalty, better polarization tracking capability, and laser linewidth tolerance compared with extended Kalman filter (EKF) with fixed Q value. Finally, in the experiment of 16 quadrature amplitude modulation system, AKF also shows a better polarization tracking capability than the EKF.
Target tracking is an important field of computer vision. The template matching tracking algorithm based on squared difference matching (SSD) and standard correlation coefficient (NCC) matching is very sensitive to the gray change of image. When the brightness or gray change, the tracking algorithm will be affected by high-frequency information. Tracking accuracy is reduced, resulting in loss of tracking target. In this paper, a differential tracking algorithm based on discrete sine transform is proposed to reduce the influence of image gray or brightness change. The algorithm that combines the discrete sine transform and the difference algorithm maps the target image into a image digital sequence. The Kalman filter predicts the target position. Using the Hamming distance determines the degree of similarity between the target and the template. The window closest to the template is determined the target to be tracked. The target to be tracked updates the template. Based on the above achieve target tracking. The algorithm is tested in this paper. Compared with SSD and NCC template matching algorithms, the algorithm tracks target stably when image gray or brightness change. And the tracking speed can meet the read-time requirement.
We demonstrate the bleaching characteristics of Cr2+: CdSe (Cr: CdSe) crystal around 2 μm and prove that Cr: CdSe crystal is an effective saturable absorber to obtain Q-switched pulsed output in Tm3+-doped fiber laser pumped Ho: YAG system. The saturable absorption property of Cr: CdSe is investigated with a pulsed source at 2090 nm. The laserinduced damage threshold of uncoated Cr: CdSe is estimated around 9.92 J/cm2 at 2090 nm with the pulse duration of 30 ns. With the measured bleaching curve, the estimated pulse saturation fluence is around 1.06 J/cm2, and the estimated ground-state absorption cross section is 8.97×10-20 cm2, which is very close to the experimental value. The preliminary laser experiments are all finished with an antireflection coated Cr: CdSe crystal to reduce the insertion loss. The maximum output pulse energy is about 1.8 mJ with repetition frequency of 685 Hz, pulse duration of 15.4 ns, and pulse peak power of 115 kW. The pulsed laser wavelength is measured to be 2090.2 nm.
A joint compensation scheme based on cascaded Kalman filter is proposed, which can implement polarization tracking, channel equalization, frequency offset, and phase noise compensation simultaneously. The experimental results show that the proposed algorithm can not only compensate multiple channel impairments simultaneously but also improve the polarization tracking capacity and accelerate the convergence speed. The scheme has up to eight times faster convergence speed compared with radius-directed equalizer (RDE) + Max-FFT (maximum fast Fourier transform) + BPS (blind phase search) and can track up polarization rotation 60 times and 15 times faster than that of RDE + Max-FFT + BPS and CMMA (cascaded multimodulus algorithm) + Max-FFT + BPS, respectively.
To deal with both of the fluctuation of background intensity and the random phase shift error, this paper present an efficient and rapid phase extraction algorithm. The parametric equations of Lissajous ellipse are derived by subtraction operations on three random interferograms. Then the elliptic parameters are calculated by ellipse fitting, which is used for phase extraction. It is unnecessary for the algorithm to calculate the random phase shift value and remove the background term, which reduces the algorithm’s complexity and shortens the processing time. The effectiveness and reliability of the algorithm are verified by both the numerical simulations and the experiment. The results shows that the algorithm is robust to the fluctuation of background intensity and modulation amplitude.
An all-fiber Fabry-Perot (FP) interferometer (FPI) sensor which can simultaneously measure strain and temperature is proposed and experimentally demonstrated. The FPI sensor is composed of a cascaded-cavity structure with a hollow-core tube fiber cavity and a standard single-mode fiber (SMF) cavity. Different cross section areas and thermal-optic coefficients of the two cavities make them differently sensitive to temperature and strain. The individual interference spectrum based on the air cavity or silica cavity can be extracted by band-pass filtering the spectrum of the sensor in frequency domain. The temperature and strain sensitivity of each cavity are obtained by tracing the wavelength shifts of the interference spectra. Furthermore, the temperature-strain cross-talk is eliminated by solving a cofficient matrix equation composed by the temperature and strain sensitivities of the two FP cavities. The strain sensitivities of two FP cavities achieved are 1.173 nm/με and 1.86 nm/με. The temperature sensitivities of two FP cavities are 0.00574 nm/°C and 0.00549 nm/°C. The advantages of the proposed sensor including simultaneous measurement of temperature and strain, no temperature-strain cross-talk, simple fabrication, and all-fiber structure make it appropriate for the real sensing applications.
We propose a joint estimation scheme for fast, accurate, and robust frequency offset (FO) estimation along with phase estimation based on modified adaptive Kalman filter (MAKF). The scheme consists of three key modules: extend Kalman filter (EKF), lock detector, and FO cycle slip recovery. The EKF module estimates time-varying phase induced by both FO and laser phase noise. The lock detector module makes decision between acquisition mode and tracking mode and consequently sets the EKF tuning parameter in an adaptive manner. The third module can detect possible cycle slip in the case of large FO and make proper correction. Based on the simulation and experimental results, the proposed MAKF has shown excellent estimation performance featuring high accuracy, fast convergence, as well as the capability of cycle slip recovery.
We present a kind of a switchable repetition rate mode-locked of bound-state solitons in a fiber laser based on Bi2Se3 saturable absorber (SA). In the fiber laser, two forms of the bound-state optical spectrum with central wavelength of 1532 nm are observed. The fiber laser is operate at the abnormal group velocity dispersion and the bound state pulses are equally distributed to the temporal domain. The fundamental cavity repetition-rate is 1.11 MHz with a pulse duration of 2.27 ps. The output average power and the pulse peak energy are 1.53 mW and 607 W respectively, which the pump power is 267 mW. The different repetition-rates are also achieved by changing the pump power or adjusting the angle of polarization controller. In the experiment, the repetition-rate is switched from 1.11 MHz to 41.32 MHz (37th-order, the highest repetition-rate).
The frequency offset estimation (FOE) schemes based on Kalman filter are proposed and investigated in detail via numerical simulation and experiment. The schemes consist of a modulation phase removing stage and Kalman filter estimation stage. In the second stage, the Kalman filters are employed for tracking either differential angles or differential data between two successive symbols. Several implementations of the proposed FOE scheme are compared by employing different modulation removing methods and two Kalman algorithms. The optimal FOE implementation is suggested for different operating conditions including optical signal-to-noise ratio and the number of the available data symbols.
A Rayleigh backscattering (RBS) assisted Brillouin erbium fiber laser scheme with multiwavelength narrow linewidth output is proposed and investigated experimentally. The stimulated Brillouin scattering and RBS take place at two conventional single-mode fibers (SMFs), respectively. RBS is used as a mechanism to compress the linewidth of each Stokes component, and it has been realized and maximized in conventional SMF by optimizing injection power of Stokes light through adjusting variable optical attenuator (VOA). By adjusting VOA attenuation, the laser can obtain three wavelengths output with 3 dB linewidth less than 2 KHz for each wavelength, or six wavelengths output with 3 dB linewidth less than 5 KHz.
We experimentally demonstrated a tunable triple-wavelength mode-locked erbium-doped fiber laser with few-layer topological insulator: Bi2Se3/polyvinyl alcohol solution. By properly adjusting the pump power and the polarization state, the single-, dual-, and triple-wavelength mode-locking operation could be stably initiated with a wavelength-tunable range (∼1 nm) and a variable wavelength spacing (1.7 or 2 nm). Meanwhile, it exhibits the maximum output power of 10 mW and pulse energy of 1.12 nJ at the pump power of 175 mW. The simple, low-cost triple-wavelength mode-locked fiber laser might be applied in various potential fields, such as optical communication, biomedical research, and sensing system.
In this paper, the performance study on the tunable multiwavelength erbium-doped fiber laser is conducted, which is
based on combination of Lyot birefringence fiber filter and nonlinear fiber loop mirror. The method to achieve its
optimal working is introduced in detail. The parameters choice based on the best tunability is analyzed from three
different perspectives: gain medium, nonlinear effect and comb filter, respectively. All the experimental results will be
given through several panels of comparison experiments. The optimal performance will finally be achieved by setting
appropriate parameters. The study in this paper will further improve the function of tunable fiber filter.
KEYWORDS: Fiber lasers, Linear filtering, Signal to noise ratio, Laser systems engineering, Mach-Zehnder interferometers, Optical filters, Polarization, Optical isolators, Switching
Serving as a frequency selective device, comb filter is a very important component to the multiwavelength erbium-doped
fiber laser. There are all kinds of comb filters, among which the Mach–Zehnder interferometer (MZI) is the commonly
used one. Since each types of Mach–Zehnder interferometers have its output features, then the study of its influence to
the output characteristics of multiwavelength erbium-doped fiber laser is necessary. In this paper, the filtering properties
of three basic Mach–Zehnder interferometer are discussed, including single-pass MZI, dual-pass MZI, dual-pass MZI
with a optical isolator embedded into the second loop. Furthermore, the working principle and tunable operation of the
tunable modified dual-pass MZI are analyzed. Above all, the influence of the four types of MZI to the output
characteristics of multiwavelength erbium-doped fiber laser is experimentally studied. The results of this paper are
helpful to understand the working principle of these comb filters and improve the output performance of
multiwavelength erbium-doped fiber laser.
A method based on the quantum-behaved particle swarm optimization algorithm is presented to design a bandpass filter
of the fibre Bragg gratings. In contrast to the other optimization algorithms such as the genetic algorithm and particle
swarm optimization algorithm, this method is simpler and easier to implement. To demonstrate the effectiveness of the
QPSO algorithm, we consider a bandpass filter. With the parameters the half the bandwidth of the filter 0.05 nm, the
Bragg wavelength 1550 nm, the grating length with 2cm is divided into 40 uniform sections and its index modulation
is what should be optimized and whole feasible solution space is searched for the index modulation. After the index
modulation profile is known for all the sections, the transfer matrix method is used to verify the final optimal index
modulation by calculating the refection spectrum. The results show the group delay is less than 12ps in band and the
calculated dispersion is relatively flat inside the passband. It is further found that the reflective spectrum has sidelobes
around -30dB and the worst in-band dispersion value is less than 200ps/nm . In addition, for this design, it takes
approximately several minutes to find the acceptable index modulation values with a notebook computer.
A fiber Bragg grating (FBG) sensor demodulation scheme based on a multi-wavelength erbium-doped fiber laser (EDFL)
with linear cavity configuration is presented and demonstrated. The scheme is one linear fiber laser cavity with two FBG
sensors as its filters. One is for strain sensing, and the other one is for temperature compensation. A power-symmetric
nonlinear optical loop mirror (NOLM) is utilized in the laser in order to suppress the mode competition and hole-burning
effect to lase two wavelengths output that correspond with two FBG sensors. The sensing quantity, which is demodulated
by spectrometer, is represented by the output wavelength shift of the EDFL with temperature and strain applying on FBG
sensors. In the experiment, strain measurement with a minimize resolution of 0.746με, i.e. 0.9pm and adjustable linear sensitivity are achieved. Due to utilizing the linear cavity multi-wavelength EDFL with a NOLM as the light source, the
scheme also exhibits important advantages including obviously high signal and noise ratio (SNR) of 40.467dB and low
power consuming comparing with common FBG sensors with broadband light as the light source.
The discrete layer peeping (DLP) algorithm has been widely used to synthesize the fiber Bragg grating for the inverse
scattering problem. The synthesis is useful both as a design tool and for characterization of already fabricated gratings
with complex profiles. In the paper, the error sources of the discrete layer peeping algorithm, including the resolution,
and the bandwidth, are analyzed. We choice different resolution and different bandwidth to calculate the reflection
spectrum of fiber Bragg gratings with different length of the fiber Bragg grating, separately. We find that the synthesized
reflectivity can all be synthesized when the resolution is different, but the length of the fiber Bragg grating required to
synthesize the reflectivity is longer as the resolution increases. For one target reflection spectrum, we also find that the
length of the fiber Bragg grating required to calculate the reflectivity with different bandwidth is almost same, and a
deviation between the target reflection spectrum and the calculated reflectivity decreases as the resolution increases. The
resolution and bandwidth required for a certain level of accuracy will depend in general on the bandwidth and the fine
structure of the initial target reflection spectrum.
KEYWORDS: Receivers, Telecommunications, Free space optics, Signal to noise ratio, Polarization, Systems modeling, Atmospheric turbulence, Turbulence, Atmospheric modeling, Free space optical communications
A theoretical model is proposed to study quantitative differences in the size of large-aperture between circle polarization
shift keying (CPolSK) and on-off keying (OOK). The quantitative differences can be analyzed with the impact from
atmospheric condition, link length, and communication wavelength. Numerical results show that FSO CPolSK systems
with longer communication wavelength can reduce the size even smaller than the systems using OOK, while it can be
not obvious with increasing link length. Meanwhile, increasing average signal-to-noise ratio (SNR) leads to a reduction
of the difference in aperture size. These results can be helpful for FSO systems design.
The influence of pump power on the output characteristics of multiwavelength erbium-doped fiber laser, which employs
the effect of the intensity-dependent loss induced by a power-symmetric nonlinear optical loop mirror, is investigated.
The results of studies show that the multiwavelength output characteristics including the number, the flatness and the
spectral region of output wavelength can be controlled by adjusting the pump power. To optimis the multiwavelength
operation, a suitable pump power must be chosen for this kind of laser.
The surface defects (indentations, humps, scores) of semiconductor wafers are the major factor to affect the performance
of the semiconductor devices. Moreover, these defects make the manufacturing process difficult or yield of the
semiconductor devices decrease. Consequently, it is necessary to do an on-line wafers detection in the benefit of the
performance and yield of the devices. Thus, developing a way suited for practical detection is the urgent affair faced to
people. The optical methods are the most suited ways for surface defects detection because of their non-contact
operation. We discuss a relatively unknown method of the light reflex surface defects detection technology (Makyoh (or
magic-mirror) topography (MT)). The optical system that we designed achieves the detection mode of the parallel light
vertical incidence for the first time. It corrects the deviation between the tradition light path and arithmetic, promotes the
detection precision. A lot of experiments based on this optical system are taken to get the difference between the
detection modes of vertical incidence and the oblique incidence. The experiments prove that the vertical incidence mode
excels the oblique incidence mode. The MT images are also analyzed and disposed. The quantitative measurement can
be realized by digital image processing technology.
A new linear cavity multi-wavelength erbium-doped fibre laser with enhanced signal-to-noise ratio characteristics is demonstrated. The laser system is developed by two steps from a conventional ring cavity configuration which consists of a frequency-shifted cavity and single multi-wavelength filters. Firstly, the noises characteristic is improved about 2.8 dB on an average with the inset of a dual-pass Mach-Zender interferometer and shifting the station of output coupler However, the output power is suppressed about 1.5 dB on an average by the change. Next, the noises characteristic is further improved by about 4.3dB against the conventional ring cavity configuration and the output power is increased by about 1.8 dB by utilizing a special Bragg grating array replacing the F-P filter to compose a linear cavity configuration.. The emitting range with output flatness better than 3dB covers 20nm wavelengths from 1540 to 1560 nm, with line spacing of 0.8nm and average output power of 0.8dBm.The linear cavity multi-wavelength erbium-doped fibre laser with high signal-to noise ratio can be useful in a wavelength division multiplexing transmission system.
An erbium-doped fiber laser with high-power and CW uniform multi-wavelength output was reported. More than 20 laser wavelengths were achieved at room temperature by using a frequency periodic filter and frequency shifter. The output spectral becomes flat after optimizing the laser cavity, the pump power and the length of active fiber. Low threshold and high slope efficiency were realized by the introduction of linear cavity.
A numerical model for multi-wavelength operation of an erbium-doped fiber ring laser with frequency-shifted feedback was presented, which based on both the standard propagation and the rate equations of a homogeneous two-level medium. The similar model has been used for the analysis of EDFA. The numerical simulations with this model provided useful information of the spectral behavior as well as important parameter for device analysis and design. This model was used to study the origin of the suppression of the EDF's homogeneous broadening due to the presence of the frequency shifter. The model was demonstrated its validity by comparing the numerical solution with experimental results, which provided the useful tool for the EDFRL device research and development.
Room temperature multi-wavelength erbium-doped fiber ring laser in the C-band is presented. Homogeneous gain broadening of erbium-doped fiber (EDF) is suppressed by adding a frequency shifter in the ring cavity. The multi-wavelength operation is demonstrated both theoretically and experimentally. High-power and extremely flat multi-wavelength output is achieved by optimizing the total laser cavity loss, pump power and fiber length, filters and concentration of the EDF.
A novel L-band multi-wavelength erbium-doped fibre ring laser was proposed and studied by numerical method. The numerical model was developed based on a C-band EDFA and the propagation and rate equations of homogeneous broaden in two levels medium. In this L-band model, the excited state absorption was included during computing. The flat multi-wavelength laser in L-band was achieved by lengthening the erbium-doped fibre, and utilizing detrimental backward amplified spontaneous emission as a secondary pump power. The laser emitting spectral region was shifted, to prevent the mode competing at room temperature. This kind of laser can be useful in a wavelength division multiplexing transmission (WDM) system.
KEYWORDS: Ultrasonography, Signal detection, Breast cancer, Ultrasonics, Signal processing, Transducers, Electronic filtering, Breast, Signal attenuation, Photoacoustic spectroscopy
Photoacoustic (PA) technique is a very important and promising biomedical diagnosis and imaging method, which can afford abundant information to analyze the pathological part of the tissue and image it. This paper proposes a new method to detect the PA wave. A focused probe ultrasonic beam was used to tag the position of PA signal and simultaneously overlapped with the PA signal, which in fact is carried out by the probe ultrasound. The overlapped signal is received by the transducer and will be further processed such as amplification and digitization. At last a compute analyzes and processes the digitized signal and the original PA signal can be restored by Fourier filtering. Furthermore, the noise of the measurement system and background could be reduced after filtering. On the basis of this method, we designed a novel setup to detect breast cancer tumor and the performance of this setup was evaluated in breast tissue-like phantom. The experiment results demonstrate the practicability of this technique.
The results of theoretical and experimental investigations of pulsed optoacoustic (PA) method for tomography of biological objects in the requency range 1-10 MHZ at the depths up to 5 centimeters are presented. Some key problems of imaging are to reduce the effect of surface PA pulse and enhance the contrast of imaging. In this paper, we propose compensation methodology to restrain the noise signal of the surface, and apply the methodology to reconstruct PA tomography,
A new method of measuring photoacoustic (PA) waves in situ is proposed. We make a probe ultrasonic beam to pass through the thick biotissue sample. Its focus point is used to tag the position of the PA signal overlapped by the PA interaction area in order to carry the PA information and take it out with the probe beam. When the detecting waves met the PA signal, a beating—wave is generated. Then it is received by a hydra-phone. After amplification and demodulation, a PA signal will be restored. In addition, the attenuation of PA signal in transmission could be decided by measuring the amplitude difference of probe ultrasound in front and behind the sample. It was helpful to simplify the reconstruction of the PA tomographic image and to increase SNR. The noise of the measurement system and background could be reduced when PA waveforms were discriminated. We measured the beating-wave produced by 532nm laser and 1 .4MHz probe ultrasonic beam in the thick biotissue and absorptive media, and reconstructed their PA signal waves with fine SNR.
A new tumor detection method by use of sonodynamic chemiluminescence was proposed in our previous work. In this paper, we further improved the diagnosis sensitivity by use of Gallium-porphyrin analogue ATX-70, one of the most active sonosensitizer found. In vitro experiments, sono-chemiluminescence of ATX-70 + FCLA system is about two times stronger than that of HpD + FCLA system. The sono-chemiluminescence was inhibited by 1O2 scavenger, but was not affected by other free radical scavenger. The mechanism of sonosensitizing was discussed. In vivo experiments, a more clearly tumor diagnostic image was obtained.
The proposed new method solves the problem that it is difficult to obtain high-resolution simultaneously in both x and y direction for an ultrasound -modulated optical tomographic 2-D image. In this method, incident laser and detector are coaxial to utilize the character of small lateral size of ultrasonic focused zone. An 860nm, 20mW laser is delivered by a fiber that passes the hole in the center of ultrasound transducer. It illuminated to a 20mm thick fat tissue with a buried object, a 5mm-wide colloidal cube, meanwhile ultrasound is focused to the sample. The scattering modulated photons are collected by an avalanche diode module, and then output signal is amplified and inputted to an oscilloscope with a FFT module. A 3D translation stage carried the sample moving to complete scanning. Combing with frequency swept ultrasound technology, the 2D tomographic images of different depth are obtained.
In this paper, we demonstrated a novel method to utilize a scattering near infrared light localized by an amplitude-modulated ultrasonic wave to image a buried object in a dense scattering medium through the synchronous scanning of the focused-ultrasound and a NIR laser beam. The frequency of the ultrasound (carrier wave) for localization of scattering light is 1MHz, and its amplitude is modulated by a low frequency sine waveform (modulation wave, 10KHz). The low frequency light signal from the focal zone of the ultrasound demodulated by real-time FFT. This scheme can increase a signal-to-noise ratio (SNR) of the ultrasound-localized-optical-tomography of tissues structure with different optical parameters. A better-quality optical tomography image of buried objects within simulating tissue is reconstructed by the detection and demodulation of the scattering light under the action of amplitude-modulated ultrasonic wave.
A new method of ultrasound-modulated optical tomography is reported, in which the buried object in optical turbid media is imaged directly with frequency-domain signals by real-time FFT. Tunable near-infrared laser is modulated by focused ultrasound. 2D tomographic images are obtained through scanning and detecting the ultrasound-modulated optical signal. Multi-wavelengths laser and diverse frequency ultrasounds are used to study image quality.
In this paper, we propose, for the first time, the concept of Sono-Dynamic Diagnosis (SDD). The novel method named FCLA Assisted Sono-Dynamic Diagnosis is designed as follows: HpD is used to localize the cancer tissue, and is sonosensitized by the ultrasound field to produce singlet oxygen. Then, another reagent, FCLA (Fluoresceinyl Cypridina Luminescent Analog), reacts with O2 to efficiently transform the chemical energy of O2 to photons, thus a strong chemiluminescence is emitted. One can then detect this emission with a high sensitive CCD imaging system to localize the tumor. Based on the principle of FCLA assisted SDD, we obtained a clear diagnostic image of a transplanted tumor in a nude mouse in the experiments. It is shown that the emission from the tumor region is much stronger than that from other regions. The outline of the tumor is quite clear. This method could have potential applications in clinics for early-stage tumor diagnosis.
A new method of ultrasound-modulated optical tomography is reported, which ultrasound wave is amplitude modulated to increase detection sensitivity and signal-to-noise rate. Near-infrared laser is incident to tissue simulating medium and modulated by focused ultrasound. A buried object in simulating medium mis imaged with modulated multi-diffuse light that pass through ultrasound focal zone. The light signal is demodulated by real-time FFT. A two-dimensional tomographic image is obtained through scanning and detecting the ultrasound-modulated optical signal.
In this paper, biological sonoluminescence (SL) of different tissues was investigated for the first time. Tissue samples (muscle, liver and fat) were prepared and put into a column- shaped ultrasound field. A photomultiplier tube and a back- illuminated cooled CCD were used to detect the SL signal. In the experiments, FCLA (Fluoresceinyl Cypridina Luminescent Analog) was used to enhance SL. With the chemiluminescence technique, we suggest that the biological SL mainly come from the free radicals produced by the ultrasound cavitation, which is different from the mechanism of the SL in aqueous solutions.
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