A Fabry-Perot cavity with chirped fiber gratings(CFGs) has been proposed and experimental demonstrated We use an ordinary single-mode fiber manufacturing two CFGs with reflection center wavelength 1549.74 nm by ultraviolet irradiation methods of phase mask method, two chirp fiber gratings with the same parameters: the length of the grating region is 10 mm, reflectivity is 95%, and bandwidth is 2.72 nm, chirp rate of 2 nm/cm, 1, 3 and 5 cm of two CFGs spacing. The Fabry-Perot (FP) cavity is composed of two CFGs as reflection faces. When an optical signal is input into the resonant cavity, the wavelength within the bandwidth of the CFGs satisfies the resonance condition, so the resonance is formed within the bandwidth. The structure is analyzed theoretically and the relationship between resonance spectrum and parameters is discussed. Wavelength changes are monitored by a spectral analyzer in real time. The experimental results show that the tunable laser output can be realized in optical communication system by changing the structure and parameters of the resonator.
A self-mixing chaotic laser which can generate ultra high frequency band is proposed.The system realize the generation of UWB through the modulation of dispersion fiber.The system enters into chaos state under optical feedback and delay feedback (the influence of dispersive fiber).In chaotic state, the Ultra bandwidth is observed on the electrospectrum analyzer by adjusting the length of dispersive fiber.In this paper, two waveforms with unimodal and bimodal are obtained by adjusting the temperature of the phase-shifting grating and adjusting the bias controller.The maximum bandwidth under single peak is 36.78GHz, and the maximum bandwidth under twin peaks is 40.57GHz.By comparison, the bandwidth generated under the bimodal peaks is larger and more complex.The experimental results show that the system bandwidth enlargement effect is very obvious in the case of the selected parameters.The system is suitable for chaotic optical communication and sensing.
A tunable self-mixing chaotic laser based on high frequency electro-optical modulation is proposed. A laser dynamics system is designed and tested for tunable chaotic laser generation and provides optical feedback and electro-optic modulation with two degrees of freedom. The chaotic laser is generated by optical feedback, and it becomes tunable by high frequency electro-optic modulation. The frequency is modulated from 0 to 6 GHz to test this system, and the spectrum of the chaotic laser is obtained with an electrical spectrum analyzer (ESA). The experimental results show the generation of a wide range of tunable chaotic lasers via electro-optic modulation. At the same time, this tunable chaotic laser has a highly sensitive dynamic response, free regulation, and wide band via adjustments in the feedback intensity and the modulation signal, and this system is proved to be suitable for applications in high-speed broadband communication and sensing.
This paper presents the design, fabrication, and characterization of a D-shaped fiber coated with polyvinyl alcohol (PVA) embedding an Au grating-based relative humidity (RH) sensor. The Au grating is fabricated on a D-shaped fiber to match the wave-vector and excite the surface plasmon, and the PVA is embedded in the Au grating as a sensitive cladding film. The refractive index of PVA changes with the ambient humidity. Measurements in a controlled environment show that the RH sensor can achieve a sensitivity of 5.4 nm per relative humidity unit in the RH range from 0% to 70% RH. Moreover, the surface plasmon resonance can be realized and used for RH sensing at the C band of optical fiber communication instead of the visible light band due to the metallic grating microstructure on the D-shaped fiber.
This paper investigates the self-mixing interference in erbium-doped fiber ring laser (FRL) and its application for
displacement and velocity sensing. Self-mixing interference in FRL with a parallel dual-channel is proposed. The
characteristics of the intensities of the laser in the dual channels with optical feedback are theoretically deduced. The
experimental results show a good agreement with the theory, and indicate that self-mixing interference with a parallel
dual-channel is an efficient approach for simultaneous multi-channel displacement measurement. Moreover, a new
method for velocity detecting based on laser speckle optical feedback injected erbium-doped FRL is presented. Random
speckle feedback causes changes in both intensity and frequency of the laser. A dynamic speckled-modulated laser
output is observed and processed by FFT analysis. A linear dependant relationship between the velocity of an object and
the mean speckle frequency defined as the ratio of the number of fluctuations is obtained, which indicates that speckle
optical feedback injected erbium-doped FRL is an effective approach for velocity detecting.
In this paper, Speckle modulating an erbium-doped fiber ring (EDFR) laser is used to detect the velocity of dynamic
diffused object. All-fiber structure of the speckle measurement system is set up. The autocorrelation function of speckle
signal related with the velocity variable of a moving object under test is theoretically derived. By experiments, the
speckle signals are acquired by a photodiode, and using the autocorrelation function, we calculated the correlation
coefficient of the speckle signals. When the coefficient is equal to 1/e, the velocity of the object is determined. In order
to explore the influence that the signal length affects on measurement accuracy, a group of signals with different length
of time is applied to calculate the velocity, and the result indicates that when signal length is greater than the correlation
length, the measurement error is very small.
A method of fabricating a colloidal photonic crystal self-assembled onto an optical fiber's cladding is proposed. The coating of a single-mode fiber was removed, the cladding was exposed, and colloidal photonic crystal was overcladding through isothermal heating evaporation-induced self-assembly. The photonic crystal cylindrical annulus is characterized by optical and scanning electron microscopy. The optical characterization was analyzed and carried out followed by detailed discussion. The measurement results show a 1545.5-nm bandgap by optical transmission spectroscopy. The results also demonstrate a practical means of enveloping macro- or microcurved surfaces with three-dimensional photonic crystals.
A new approach for velocity detecting based on laser speckle feedback injected erbium-doped fiber (EDF) ring laser is
presented in this paper. 1550nm wavelength light is outgone through an optical fiber and shoots onto a moving object by
a lens. Portion of the light scattered from the object produces dynamic speckle, when it is back-coupled into the same
fiber and injects the EDF ring laser, random intensity feedback causes changes of both intensity and frequency of the
laser. We theoretically analyzed the laser output when speckle feedback injects an EDF ring laser by using model of the
injection-seeded EDF ring laser, and experimentally obtained the dynamic speckle-modulated laser output signal by a
photodiode (PD). The signal is analyzed by way of FFT analysis, and the mean speckle frequency (MSF), which is
defined as the ratio of number of fluctuations in the detected signal to the measurement time, is obtained. We studied the
relationship between the velocities and MSFs by changing the velocity of object, thus a linear dependent relationship
between them is obtained, which indicates that speckle feedback injected EDF ring laser is an effective approach for
velocity detecting, it is promising to develop a new generation of optical fiber active sensor.
In recent years, active sensing, which emits radiation directed toward the target to be investigated, has attracted more and
more attention. Laser is not only as a light source, but also as a sensitive element viz. sensing source presented in the
active sensing system which based on the theory of self-mixing interference in this paper. This application can make the
sensing system more simple, compact, and less cost. In this paper, we propose the active sensing by the combination of
DBR lasers and the self-mixing interference technique. The self-mixing interference in DBR lasers based on the study of
F-P cavity and coupling wave equations has been analyzed. Three self-mixing interference models in DBR lasers are
presented, and one of them has been taken for instance to simulate the output variations of self-mixing interference. The
influence from different internal or external parameters on the output variations and the inclination degree of waveform
of the active sensing were discussed in simulation also. And thereby good signal of self-mixing interference in DBR
lasers can be obtained. This application can satisfies the request of microminiaturized sensing device and the demand of
interrogation of optical fiber, and predigests the structure of sensing system.
Self-mixing interference in DFB-LD for fiber sensing application has been analyzed in this paper. Due to the characteristics of good model and narrow spectrum, the DFB-LD has the application potentiality in the filed of self-mixing interference, and optical communication technique has rapidly driven the development of optical fiber sensing technique. The combination of self-mixing interference technique and optical fiber sensing technique can satisfy the request of microminiaturized sensing device and the demand of interrogation of optical fiber. It is possible to form a novel optical fiber sensing measurement network, and the combination is helpful to the application at the aspects of avigation, industrial automation, medical examination, etc. In this work, based on the theory of coupled wave, the variation of laser output caused by self-mixing interference has been presented. For optical fiber sensing application, the self-mixing interference under the condition of transmitting the external optical signal by fiber has been analyzed. The influence from the variation of attenuation caused by the increment of fiber length and the reflectivity of the remote target to the output signal of self-mixing interference has been discussed in numerical simulation.
The statistical analysis and experimental results of self-mixing speckle interference in the distributed feedback (DFB) laser are presented in this paper. Dynamics solution of output gain variation in the DFB cavity is deduced on the basis of speckle theory and self-mixing interference in the DFB laser, when external optical feedback comes from a moving rough surface. By numeric simulations and experiments, the dynamic output variations of the DFB laser as well as their probability density functions (PDFs) are analyzed. Both results of simulations and experiments are in agreement with each other. The experimental results show that this speckle signal processing can be used to measure velocity of target.
CCD micrographic optical system is applied to observing and measuring Newton’s rings. The reduction of the resolving power for the micrographs can be compensated by image processing. Contrasting with the JXD-1 microscope, on condition that the measuring precision is alike, CCD instrument of Newton’s ring has the better observing effect, its visual field is enlarged to 2.5 times, the date can be collected more conveniently and there are no outside disturbs. By setting up the rule, this instrument can be more suited to the demands of the optical experimental teaching for today’s university.
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