Fiber-optic oscillator

 

(57) Abstract:

Fiber-optic oscillator can be used in the transducers of physical quantities to measure temperature, pressure, acceleration. The oscillator contains a fiber-optic laser, one end of the optical fiber is coupled to the collimator forming a parallel beam of light to the reflecting surface of the microcavity. The second end of the optical fiber, an output, forms together with the reflecting surface of the microcavity two-mirror optical resonator fiber optic laser. The reflective surface of the microcavity is under some given angle to the axis of the beam. Self-oscillating mode in the system of fiber-optic laser - microresonator is due to modulation of the amplitude of the reflection coefficient of the optical resonator fiber laser or q-switching two-mirror optical resonator due to photoinduced angular deviations of one of the mirrors, which serves as the reflecting surface of the microcavity. Stable measurement results. 2 Il.

The invention relates to fiber optic priorisation, excited by light.

The creation of a new class of fiber-optical oscillator based on micromechanical resonator (Mr) and optical coherent radiation interacting with MP. In the literature reported the development of various schemes for optical excitation of vibrations Mr and their practical implementation.

In all cases, the intensity modulation of optical radiation occurs at the resonance frequency of the MRI.

When it absorbs MP optical radiation of its illuminated side is experiencing thermal expansion, resulting in Mr occurs bending moment varying in phase with the modulated optical radiation, which leads to mechanical vibrations at the resonance frequency of the MRI.

External influences (temperature, pressure, acceleration, etc.) is converted into the internal stress MRI, which leads to change of its own resonant frequency determined by the dimensions of the Mr and its physical properties.

In connection with the small amplitude oscillations Mr ( 0.1 ám) in the oscillator is applied interferometric method for obtaining information about the resonances of h is retronym mirror, either end of the light conductor, paired with a reflective surface Mr.

Direct communication with a digital measuring device without converting the analogue-dial, large extent of the optical transmission channel, high potential accuracy of the measurement of the resonance frequency make this type of sensors is promising.

However, a microresonator oscillator based on photometric Mr excitation and optical detection of oscillations, have the following disadvantage.

The position of the working point of A Fabry-Perot interferometer unstable and shift depends both from the drift of the main characteristics of the Mr, and the instability of the radiation source and the parameters of the Fabry-Perot interferometer. In other words, the performance of the oscillator is affected by both the instability characteristics of the channel of the Mr excitation and channel interferometric information retrieval that requires special measures to stabilize the position of the working point A.

Closest to the proposed technical solution to the technical essence and the achieved results is a fiber optic sensor (WATER) physical led is microresonator with the reflecting surface, the photodetector and the spectrum analyzer.

The known solution is characterized by the following negative characteristics:

- high stability requirements power source (the pump current of the laser diode) and careful control of the operating point of the Fabry-Perot interferometer due to changes in the small limits of optical radiation power incident on Mr;

additional loss of optical power caused by the presence of the necessary discrete elements forming an additional feedback channel in the electronic circuit;

- stringent requirements on the stability characteristics of the resonator Fabry-Perot, and characteristics of Mr in because of the limited possibilities of their correction in this electronic scheme;

- limited adjustment of the working point of the Fabry-Perot interferometer by changing the wavelength of the optical radiation of the laser diode when implementing complex electronic circuits reverse the positive connection.

The problem solved by this invention is the development of a microresonator oscillator on the basis of fiber-optic laser and the q-switching two-mirror optical resonator wines the end of a single-mode optical fiber is interfaced with the collimator, forming a parallel light beam on the reflective surface Mr, oriented at an angle to the optical axis of the incident beam, and the second is the output.

Changing the output power with the reflection from the Mr results, due to the effect of photoinduced deformation, to the modulation of the deflection angle of the reflected beam (t), i.e., the modulation of optical power.

As a collimator uses a gradient rod lens (GSL) and a quarter of a period, forming a Gaussian beams.

Regardless of the topology and design of the Mr under certain conditions in the considered scheme is established self-oscillating mode with frequency F, which practically coincide with the resonant frequency f = f

These conditions are formulated in the following way:

in the initial state, the deflection angleandthe reflective surface Mr is in the interval1and2limits (1,2) depend on the characteristics of Mr and optical fiber laser;

resonance frequency of the Mr is close to the frequency of the relaxation oscillations of fiber-optic laser fRelor its harmonics, i.e., f nfRelwhere n = 1,2,3... Note that fRelthe Oprah
- average radiation power exceeds a certain threshold level is dependent on characteristics of the Mr and fiber laser.

As a result of the system Mr - fiber-optic laser self-oscillations at the resonant frequency of the Mr, there is no need to introduce interferometric feedback stabilization of the operating point of the oscillator.

The solution of this problem is provided by the fact that in a microresonator optical fiber oscillator containing a source of optical radiation, microresonator, as the source of optical radiation used fiber-optic laser, one end of the optical fiber is coupled to the collimator interposed between this end and the microcavity, and the second end of the fiber is an output, while the reflective surface forms a microcavity with an output end of the optical fiber, the two-mirror optical resonator fiber laser and the reflecting surface of the microcavity in the initial position is oriented to the optical axis of the collimated beam at some given angleand. Optical radiation optical fiber laser using a gradient rod Lin is Roy makes with the optical axis of the incident beam some angleandwhen the output signal of the oscillator is simulated resonant frequency of the Mr due to modulation of the q-switched two-mirror optical resonator fiber laser.

The essence of the proposed solution is the development of a microresonator optical fiber oscillator, in which the excitation of self-oscillations uses fiber-optic laser without introducing additional optical fiber devices, while for the existence of oscillatory modes in the system fiber-optic laser - microresonator sufficient modulation amplitude reflection coefficient R of the optical resonator fiber-optic laser arising from the fluctuations of the microcavity.

Fiber optic laser is a segment of single-mode type optical fiber of length L, the pumping can be performed in various ways, for example through the segment buffer of non-activated fiber, is perfectly consistent with carbon fiber.

The unique properties of the fiber-optic laser to achieve the effective optical approval of Mr with fiber-optic laser, and t is istoricheskikh materials such as Si, SiO2, CaAs allow you to implement the Mr structure with the specified acoustic performance and topology (for example, in the form of micromembrane, micromastia, microconsole and so on), allowing the system Mr - fiber-optic laser self-oscillations, resonance frequency which depends on the impact of relevant external factors (temperature, pressure, acceleration, and others).

In Fig. 1 presents a diagram of a microresonator optical fiber oscillator of a new type, where 1 - fiber-optic laser, erbium activated, pumped at a wavelength ofn= 0.98 μm, 2 - single-mode fiber, 3 - collimator, which was applied gradient rod lens in the fourth period, forming a Gaussian beams with parameters : diameter of the waist of the beam 2 Wo= 780 μm, the angle of divergence 2 = 2,6 10-3happy 4 - mirror M1optical resonator, which serves as the interface of the fiber-air, 5 - microresonator representing silicon membrane (micromattic, there), obtained by means of anisotropic etching, 6 - angleandbetween the normal to the reflective surface Mr and optical axis of the light beam, to form the device operates as follows.

Part of the power of the optical beam generated by the collimator 3, is reflected from the surface 7 of the microcavity 5, the normal to which in the initial position is the angleandwith the axis of the beam of light, and back into the resonator fiber laser.

Changing the output power fiber-optic laser W1falling on MRI results due to the effect of photoinduced deformation to the modulation of the deflection angle of the reflected beam (t) i.e., modulation of [(t)].

In Fig. 2 shows the experimental dependence (). Experimental results showed that regardless of the topology and design of MRI while performing the specified conditions (which were discussed above) in the device is self-oscillating mode with a frequency of Mr f F.

The experimental results obtained for the Mr in the form of micromastia size 1650 x 400 x 6 μm3with a film of Nickel (Nias reflective coatings MP. The film thickness was hNi0.3 μm, the reflection coefficient is 72%. Due to the considerable width of the Mr ensured its effective interaction with the optical beam. In the present case was instituted self-oscillations with frequencies F1= 35,5 to the activity was 1.5...4 mW, the ratio of signal to noise in the system 40...50 dB. The amplitude of Mr was 30 nm. Q-switched data modes measured with the acoustic excitation of vibrations, was 90 and 120, respectively.

As can be seen from Fig. 2, the region of existence of self-oscillations (1,2for the main oscillation modes is located entirely on one branch of the curve ().

This indicates that the q-switched optical resonator caused by the modulation of the beam deflection angles, and not an extra focusing (defocusing) due to the curvature of the surface of the Mr with self-excited oscillations. In addition, the experiment showed that when the dimension of H as in the submicron range, and significantly ( 1.5 mm) breakdown of self-oscillations were observed, with the relative change of the frequency F/F was 310-4. Within the interval (1,2) observed weak dependence of F(and), the nature of the monotony of which depends on the angular and linear geometric parameters describing the spatial orientation of the optical beam relative to the MP. Width of interval = O2-O1depends on the angle of divergence of the beam, and the greater the angle of divergence, the less the width of the interval. If this method of excitation of self-oscillations for the effective interaction of fiber-optic laser microcavity requires the use of detergents sizes, comparable to the diameter of the collimated beam. The linear increase of the geometrical sizes of a microresonator converters leads to significant changes of the conversion.

Thus, a new principle of construction of a microresonator optical fiber oscillator, thus to stabilize the operating point of the oscillator does not require the introduction of additional optical devices in the optical fiber laser.

Self-oscillating mode in the system of fiber-optic laser - Mr is carried out by modulation of the amplitude of the reflection coefficient R of the optical cavity fiber laser, or the q-switching two-mirror optical resonator due to photoinduced angular deviations of one of the mirrors, which serves as the reflective surface Mr.

Fiber-optic oscillator containing a laser source of the optical radiation from the optical fiber and microresonator, and one end of the light guide is associated with a collimator interposed between this end and the microcavity, and the second end of the fiber is an output, wherein the laser source opticoat with the exit end of the light guide two-mirror optical resonator fiber laser, and the reflecting surface of the microcavity in the initial position is oriented to the optical axis of the collimated beam at some given angleand.

 

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