In this paper a new optimum design method of anisotropic acousto-optic deflector (AOD) with ultrasonic beam steering
is introduced for two kinds of crystals: Tellurium Oxide (TeO2) and Lithium Niobate (LN). First anisotropic
acousto-optic (AO) interaction geometric relationships in the two crystals are calculated. Then optimum design method
and results, including design parameters and design curves of the two anisotropic AOD, are given through calculating
Bragg loss vs acoustic frequency. Final curves of relative bandwidth vs relative length for the two anisotropic AOD are
given. Compared with non-steering AOD, when relative bandwidth is equal to octave bandwidth, the relative length of
steering AOD will increase 34.7% for TeO2 anisotropic AOD and 73.4% for LN anisotropic AOD, when relative length
is satisfied condition into Bragg region, the relative bandwidth of steering AOD will increase 9.1% for TeO2 anisotropic
AOD and 17.7% for LN anisotropic AOD.
Lithium Niobate (LN) and Quartz. crystal are good piezoelectric crystals, they can be used bases of surface acoustic
wave (SAW) devices. In this paper, SAW elemental equation and corresponding mechanics boundary condition
equation are deduced. For the above two crystals, SAW velocities are calculated systematically, and curves of the
acoustic reciprocal velocity are drawn using a new circle iterative method in decoupling acoustic sagittal plane, that is
yz plane. Calculation results lay a good theoretical base for design of SAW devices and have research signification and
In this paper a strengthened acousto-optic (AO) coefficient of piezoelectric crystal is proposed. It shows the influences of AO effect, electro-optic (EO) effect and piezoelectric effect in piezoelectric crystal. Through correcting acoustic momentum mismatch into sum of the acoustic and electric momentum mismatch, the coupled wave equation group of the surface acoustic wave (SAW) AO effect can be changed as that of SAW acousto-electro-optic (AEO) effect. A diffraction efficiency formula of SAW AEO effect is given through solving the equation group. The formula indicates that the diffraction efficiency is related to power of SAW, acoustic frequency deviation and direct current (DC) voltage. We designed and manufactured a SAW AEO device using Lithium Niobate (LN). Some curves of relative diffracted efficiency vs power of electric signals driving the device, acoustic frequency deviation and DC voltage are measured. Experimental results are consistent with theory. SAW AEO device can be used as a deflector or modulator. When it is used as deflector, its bandwidth is wider than that of SAW AO deflector. When it is used as modulator, its center frequency can be changed. SAW AEO device has smaller volume, less energy consume and is easy to integrate. It can be used in optic communication and real time signal processing, for example correlation, convolution, spectrum analysis and optic vector calculation and so on.
Wavelength encoding sensors, such as fiber Bragg grating, have the advantage of strong antijamming ability. However,
the wavelength encoding signal is usually converted into electric intensity signal by demodulators in most
measurements. The intensity signal is easy to be disturbed by environmental factors, so the advantage of wavelength
encoding fails due to the instable intensity demodulation. In this paper, a novel wavelength demodulating method is
presented. This method demodulates the wavelength encoding signal directly by means of counting using a Sagnac
interferometer with birefringent fiber without the encoding conversion from wavelength to intensity. Through the
interferometer, the changed wavelength signal from sensor becomes the kind of output light, the intensity of which is
changed with wavelength periodically. The intensity can easy be disturbed, but its period is very stable. In other words,
the change of wavelength in one intensity period is stable. With this character, we count the number when the rising edge
and falling edge of intensity appear, and then calculate the accurate change of wavelength signal. In experiment, we get
the 0.01 nm wavelength resolution by use of a Sagnac interferometer with 200 meter birefringent fiber. It can be proved
that the intensity frequency (the reciprocal of intensity period) changed with wavelength is proportional to the length of
birefringent fiber. The length is fixed, the frequency is determined. For farther increasing the wavelength resolution, it is
only necessary to increase the length of birefringent fiber. The wavelength demodulator by counting method has high
stability and high precision.
A strengthened acousto-optic (AO) coefficient of piezoelectric crystal is defined. AO coupled-wave equations of surface
acoustic wave (SAW) to plane guide optic wave (PGOW) and to fiber guide optic wave (FGOW) are given respectively.
A diffractive efficiency formula of SAW PGOW AO interaction and a back-wave efficiency formula of SAW FGOW
AO interaction are given. The formulas indicate that under condition of weak AO interaction intensities of the
diffractive wave and the back-wave are proportional to ultrasonic powers. Lithium Niobate (LN) is optimum crystal of
SAW PGOW AO device, quartz is optimum crystal of SAW FGOW AO device. A SAW PGOW AO modulator using LN
and a SAW FGOW AO modulator using quartz are designed and manufactured. Some curves of the diffractive wave
power and the back-wave power vs. electric powers of signals driving the modulators are measured. SAW AO
modulators have many advantages, for example small volume, good stability, low energy consumption and it is easy to
integrate. The modulators can be used as intensity modulators. The modulators have applications in optic communication and real time signal processing.
It is well known that as a measurement device, Sagnac fiber interferometer has the advantages of high measuring
sensibility and strong antijamming ability. However, it is precisely because of the high sensibility, the measured change
range of sensed quantities is usually very small. And also because of the strong antijamming ability, the fiber of Sagnac
interferometer can not be used as a sensor. The reason is that the sensed signal well be eliminated by the signal
cancellation effect between the two directions in Sagnac interferometer like the disturbance signal. This paper presents a
novel Sagnac fiber sensor. It is added two devices into the common Sagnac fiber loop, one is the phase compression
device and another is the birefringent fiber sensor. The phase compression device consists of a time delay fiber and a
piezoelectic ceramic twisted around by Sagnac fiber. This device can realize the phase compression by which the
measured range of sensed quantities is widely extended. The birefringent fiber sensor consists of a short section of high
birefringent fiber. The method of adding the birefringent fiber sensor is selecting suitable position on Sagnac fiber loop
and breaking off the fiber, then melting and linking the two break surfaces with the short section of high birefringent
fiber. Not like the common fiber, there is not cancellation effect on the birefringent fiber. So the Sagnac interferometer
can become a sensor. This kind of Sagnac fiber sensor has the advantages of high measuring precision, wide measured
range, strong antijamming ability and simple structure.
Wavelength encoding sensors, such as fiber Bragg grating, have the advantage of strong antijamming ability. However,
the wavelength encoding signal is usually converted to electric intensity signal by demodulators in most measurements.
The intensity signal is easy to be disturbed by environmental factors, so the advantage of wavelength encoding fails due
to the instable intensity demodulation. In this paper, a novel wavelength demodulating method is presented. This method
demodulates wavelength encoding signal directly by means of counting using a Sagnac interferometer with birefringent
fiber without encoding conversion from wavelength to intensity. Through the interferometer, the changed wavelength
signal from sensor becomes the kind of output light, the intensity of which is changed with wavelength periodically. The
intensity can easy be disturbed, but its period is very stable. In other words, the change of wavelength in one intensity
period is stable. With this character, we count the number at the rising edge and falling edge of intensity appear, and then
calculate the accurate change of wavelength signal. From experiment, we get 0.067 nm wavelength resolution by use of a
Sagnac interferometer with 30 meter birefringent fiber. It is proved that the intensity frequency (the reciprocal of
intensity period) changed with wavelength is proportional to the length of birefringent fiber. If the length is fixed, the
frequency is determined. For farther increase of wavelength resolution, it is only necessary to increase the length of
birefringent fiber. The wavelength demodulator is characteristic of high stability and high precision.
In this paper, a fiber coupled-mode equation between front-wave and back-wave of optical guided modes with micro disturbance is given from parameter interaction equation. Considering surface acoustic wave (SAW) as the micro disturbance, a coupled-wave equation group of SAW all-fiber acousto-optic (AO) effect is deduced. The equation group includes front-wave equation and back-wave equation. A back-wave efficiency formula is demonstrated through solving the equation group. It is proved, that the back-wave efficiency is directly proportional to power of the SAW under condition of weak AO interaction. Quartz crystal is considered as the best base crystal. It is because acoustic impedances of the quartz crystal and the fiber are equal approximately. According to form of SAW basic equations or Christofell equations the best SAW mode of the quartz is determined. All-fiber AO intensity modulator using SAW is designed and manufactured. Modulation curve of optic power of the back-wave vs power of electric signals driving the device is measured. The experimental results indicate, optic power of the back-wave is directly proportional to power of electric signals driving the device. The experimental results are consistent with the theory. Advantages of the device are smaller volumes, less energy consumes, less inset-losses and so on. Besides, it is easy to integration and can be used in optic fiber communication.
Because of the characteristic of wavelength encoding, fiber Bragg grating (FBG) has the advantages of immunity to light
power fluctuation, variation in polarization and connecting loss, so it has high sensing precision. However, for the
demodulation of FBG, wavelength signal is usually converted to electric amplitude signal. By measuring the amplitude
signal, the sensing result is obtained. It is well know that the amplitude signal is easy to be disturbed in sense. For this
reason, amplitude demodulation limits the effect of wavelength encoding of FBG. This paper presents a novel method of
counting wavelength demodulation for FBG sensors using a high birefringent fiber (HBF) loop mirror. This demodulator
has simple structure, high precision, low cost and convenient to use. The resolution of the loop mirror device with 30
meter long of HBF is 0.067 nm. This counting wavelength demodulating method has the significance for widespread
practical application of FBG sensors.
Time-division-multiplexing(TDM) demodulation technique of Fiber Bragg Grating(FBG) sensor arrays based on a
tunable pulsed laser is studied. A tunable fiber laser based on a matched FBG is applied, and the wavelengths of the
sensing FBGs are obtained by determining the maximum voltages by using a photodiode. The advantages of this scheme
include simple structure, high signal-to-noise ratio, and the sensing signals are obtained by determining the maximum
A Fiber Bragg Grating (FBG) sensor demodulation system of matched Bragg gating with a simple structure is studied. The cantilever is designed by using acryl glass, and the wavelength's linear tuning of FBG is operated by tuning the cantilever of acryl glass. The sensor signal of Real-time detect is detected by using an oscilloscope after the optical sensor signal enters the photoelectric detector. Demodulation operation of matched-gating is achieved. Wavelength resolution of 2.33pm is obtained. The advantages of this demodulation system is simple structure, electromagnetic interference resistance, high wavelength resolution and high rate of cost performance, so it has a great application prospect.
A high-sensitivity fiber Bragg grating (FBG) pressure sensor has been designed and studied. Confining some gas inside a glass cylinder with a close glass piston which can move smoothly along the cylinder, and sticking two ends of a fiber Bragg grating on the outer side of the cylinder and piston respectively. The variation of the external pressure results in the change of the tension that the fiber grating is subjected to and then the pressure can be measured by the measurement of the Bragg wavelength of the FBG. The pressure sensitivity coefficient is up to -0.7676/MPa, which is about 3.88×105 times the value of bare fiber Bragg gratings, the highest sensitivity ever reported. The sensor can be used to potential applications in the measurement of air pressure, hydraulic pressure and vibration in the range of low pressure.
A smart temperature sensor is performed based on the high birefringence (HB) fiber loop mirror. The sensing can be achieved by simply detecting the light intensity, utilizing a single mode laser diode (LD) as the source. In the range of 25°C-35°C, the resolution and linear regression are 0.05°C and 0.9986, respectively. The sensor can be employed to precise temperature measurement and the range can expand further when selecting shorter HB fiber in the loop mirror.
The time resolved propagation of ultrashort Gaussian beams laser pulses within turbid tissues is simulated by a Gaussian integrated methods. The various rules of the ultrashort pulse at different shape and pulsewidth in semi-infinite boundary conditions versus the turbid tissues for various scattering coefficients μs, absorption coefficients μa, scattering phase functions ρ(Θ), and the average cosine of the scattering angle g are presented.
In this paper we researched principles of three-dimensional (3-D) isotropic acousto-electro-optic (AEO) modulator, including coupled wave equations and diffraction efficiency formula of the 3-D AEO effect. The AEO crystal is worn into a column of six side-faces. Three transducers are stuck on adjacent side-faces and they can produce three acoustic energy channels of 60° each other in acoustic plane. Direct current (DC) electrodes with central holes are plated on the end-faces. Through the hole, incident light propagates along axis of the column, which is perpendicular to the acoustic plane. So the acousto-optic (AO) effect must be Raman-Nath effect, it can realize 3-D light deflection. The DC electric field is supplied along the axis of the column too. So the electro-optic (EO) effect must be longitudinal, it can realize light modulation. We designed and made a 3-D isotropic AEO modulator of centre frequency 50 MHz using Potassium Hydrogen Phosphate (KDP) crystal, and measured its modulation curve of relative diffraction efficiency vs DC voltages. Measured results agree with theoretical calculation. Multi-dimensional AEO modulator has applications in multi-channel optic communication and optic signal processing.
In this paper, a filter which is cascaded n-stage high-birefringence fiber loop mirrors is presented. The related theory is analyzed and an expression cascaded with n-stage high-birefringence fiber loop mirrors of output intensity is given. Since experiment results are consistent with simulation outcomes, our theory is proved. Compared with a single stage high-birefringence filter, the cascaded filter shows more complex transmission Characteristics. Therefore, this kind of filter is flexible transmission spectrum and low cost for manufacture.
A TDM FBG sensor system with CCD detection was presented for a serial FBG array. Four FBGs were multiplexed and a device based on NOLM technique was adopted for the separation of the pulses. Computer simulation shows that the system provides high sensitivity which is the main factor for a practical FBG sensor.