CN105136336B - A kind of optical fiber air ring cavity temperature sensor based on femto-second laser - Google Patents

Abstract

The present invention provides a kind of optical fiber air ring cavity temperature sensor based on femto-second laser, it is characterised in that：It is made of incident optical (1), air ring cavity configuration (2), the output optical fiber (3)；The both ends of air ring cavity configuration (2) are connected with incident optical (1) and the output optical fiber (3) respectively；Incident optical (1) collectively forms all -fiber Mach-Zehnder interferometer with air ring cavity configuration (2) with the output optical fiber (3)；High sensitivity of the present invention, structure is small, can be applied in various pyrometric Practical Projects.

Description

A fiber optic air ring cavity temperature sensor based on femtosecond laser

technical field

The invention provides an optical fiber air ring cavity temperature sensor based on a femtosecond laser, belonging to the technical field of optical fiber sensing.

Background technique

The Mach-Zehnder interferometer is widely used in the field of sensing, and it is made by using the principle of double-beam interference. The traditional Mach-Zehnder interferometer requires two single-mode optical fibers of the same length, which are easily affected by other physical quantities such as humidity in addition to the physical quantities that need to be measured. It can be seen that the traditional Mach-Zehnder interferometer is difficult to manufacture. Therefore, the all-fiber Mach-Zehnder interferometer was proposed. The current all-fiber Mach-Zehnder interferometer is mainly based on the structure of FBG, LPFG, PCF, optical fiber puller, optical fiber dislocation connection, etc. Although the sensitivity is high, the temperature sensor composed of these Mach-Zehnder interferometers is large in size and difficult to reuse. In order to solve the above problems, a new type of all-fiber Mach-Zehnder interferometer is proposed. The fabrication of this temperature sensor uses a femtosecond laser, which is used for precision micro-nano processing. When it interacts with matter, It can realize ultra-high resolution and ultra-high precision, so as to achieve nanoscale processing and manufacturing. This all-fiber Mach-Zehnder interferometer has the advantages of high sensitivity and tiny structure.

The air ring cavity structure in the fiber air ring cavity temperature sensor based on the femtosecond laser makes the light that originally only transmitted in the fiber core transmit and interfere in the form of the core mode and the air ring cavity mode respectively. When the sensor is used to measure the temperature of the external environment, the interference fringes will drift every time the temperature is changed. This is because the air ring cavity mode and the fiber core mode respond differently to temperature changes, which causes the original optical path difference to change. As the optical path difference changes, the interference fringes will change. After a series of temperature changes, a series of corresponding interference fringes can be observed on the spectrometer. In some characteristic positions of the interference fringes, such as interference peaks or interference valleys, it can be seen that the wavelength where the extreme value is located has shifted, and temperature measurement can be realized by monitoring the drift of the interference spectrum.

Contents of the invention

The object of the present invention is to provide an optical fiber air ring cavity temperature sensor based on a femtosecond laser. The device can convert the variation of the temperature to be measured into the wavelength drift of the detection signal. It has the advantages of high sensitivity, small structure and easy repeated use.

The present invention is realized through the following technical solutions:

A fiber optic air ring cavity temperature sensor based on a femtosecond laser, consisting of an incident optical fiber (1), an air ring cavity structure (2), and an outgoing fiber optic (3); the two ends of the air ring cavity structure (2) are respectively connected to the incident optical fiber (1) is connected to the outgoing optical fiber (3); the incoming optical fiber (1), the air ring cavity structure (2) and the outgoing optical fiber (3) together constitute an all-fiber Mach-Zehnder interferometer.

A kind of optical fiber air ring cavity temperature sensor based on femtosecond laser is characterized in that: the incident optical fiber (1) and the outgoing optical fiber (3) can all adopt G.652 single-mode optical fiber, and the incident optical fiber (1) and the outgoing optical fiber (5) The length is 20-40 cm.

A kind of optical fiber air ring cavity temperature sensor based on femtosecond laser is characterized in that: the optical fiber used in the air ring cavity structure (2) can adopt G.652 single-mode fiber, the length is 50um～100um, the air ring cavity The outer circle radius of the cavity structure (2) is 4um-7um, and the inner circle radius is 2um-5um.

The working principle of the present invention is: when the light emitted by the broadband light source reaches the air ring cavity through the incident fiber, the core diameter of the incident fiber is thicker than that of the section of the fiber in the air ring cavity structure. In this way, the light originally transmitted in the fiber core is divided into two parts, one part of the light enters the air ring cavity, and the other part of the light will continue to transmit along the fiber core. When reaching the end of the air ring cavity structure, the light transmitted in the air ring cavity The light will interfere with the light propagating in the core, and finally travel through the exit fiber to the spectrometer.

The light transmitted between the fiber core and the air ring cavity interferes. Simply put, the interference between the fiber core and the air ring cavity can be obtained by a known formula:

Among them, I _core and I _cavity are the light intensity of the light transmitted from the fiber core and the air ring cavity structure respectively, λ is the wavelength of the incident light, L is the length of the air ring cavity, is the effective refractive index difference between the core mode and the air ring cavity mode, is the initial phase of the interference. Since L is a constant, the formula for the temperature sensitivity of this Mach-Zehnder interferometer is

in and are the temperature coefficients of the refractive index of the fiber core and the air medium, respectively. The effective refractive index of the air ring cavity remains unchanged at different temperatures, so the temperature coefficient of the fiber core refractive index determines the temperature sensitivity of the Mach-Zehnder interferometer.

When the sensor is used to measure the external temperature, every time the external temperature is changed, the optical path difference between the air ring cavity mode and the fiber core mode changes due to the different response degrees of the air ring cavity mode and the fiber core mode to the temperature, thus The phase difference between the air ring cavity mode and the fiber core mode is changed, and the interference fringe drifts, and the signal to be measured can be restored by monitoring the wavelength drift of the interference spectrum.

The beneficial effect of the present invention is that: the temperature sensor is manufactured based on an interconnected Mach-Zehnder interferometer with an air ring cavity structure. The light transmitted in the fiber core is divided into two parts, one part of the light enters the air ring cavity, and the other part of the light will continue to transmit along the burnt fiber core. When reaching the end of the air ring cavity structure, the light transmitted in the air ring cavity will Interference with light propagating in the core. When changing the ambient temperature of the sensor, the corresponding interference spectrum will drift. The sensor uses an internally connected Mach-Zehnder interferometer, which has better stability, higher sensitivity, and is less susceptible to external refractive index changes.

Description of drawings

Fig. 1 is the schematic diagram of the fiber-optic air ring cavity temperature sensor based on femtosecond laser of the present invention;

Detailed ways

Below in conjunction with accompanying drawing and embodiment example, the present invention will be further described:

Referring to accompanying drawing 1, a kind of fiber-optic air ring cavity temperature sensor based on femtosecond laser is made up of incident optical fiber (1), air ring cavity structure (2), outgoing optical fiber (3); two of air ring cavity structure (2) The ends are respectively connected with the incident optical fiber (1) and the outgoing optical fiber (3); the incident optical fiber (1), the air ring cavity structure (2) and the outgoing optical fiber (3) form an all-fiber Mach-Zehnder interferometer. The manufacturing process of the air ring cavity structure (2) is as follows: use a femtosecond laser to drill holes on the end face of the optical fiber, adjust the laser spot diameter to about 2um, and drill a circle of small holes along the fiber core in the cladding, each small hole There is a cross in between. At the same time, the intensity of the femtosecond laser and the distance of the focal point are adjusted to control the depth of the small hole. Therefore, an annular air cavity is formed at the interface between the core and the cladding. After the hole is drilled, because the inner surface of the annular air cavity is not smooth enough, HF is used to corrode the optical fiber to make it smooth. Next, the end faces of the air ring cavity structure (2) are respectively connected with the incident optical fiber (1) and the outgoing optical fiber (3).

The working mode of the device of the invention is as follows: one end of the temperature sensor is connected to a broadband light source, and the other end is connected to a spectrometer. When the light emitted by the broadband light source reaches the air ring cavity structure through the incident fiber, the light originally transmitted in the fiber core is divided into two parts, one part enters the air ring cavity, and the other part will continue to transmit along the fiber core. At the end of the ring cavity structure, the light propagating in the air ring cavity will interfere with the light propagating in the burned core. When changing the external temperature of the sensor, the corresponding interference spectrum will drift, so that the sensitivity of the sensor can be obtained.

Claims (3)

1. a kind of optical fiber air ring cavity temperature sensor based on femto-second laser, by incident optical (1), air ring cavity configuration (2), the output optical fiber (3) forms；The both ends of air ring cavity configuration (2) are connected with incident optical (1) and the output optical fiber (3) respectively It connects；Incident optical (1) collectively forms all -fiber Mach-Zehnder interferometer with air ring cavity configuration (2) with the output optical fiber (3)；It is special Sign is that air ring cavity configuration (2) is to make a call to a circle aperture along fibre core in the covering of single mode optical fiber end face with femto-second laser, There is intersection between each aperture, while adjusting the depth of the intensity and focus point distance control aperture of femto-second laser, it is ensured that is fine Core forms annular air chamber with covering circle intersection, reuses hydrofluoric acid corrosion annular air chamber, makes its smooth surface, and will Fibre core attenuates.

2. a kind of optical fiber air ring cavity temperature sensor based on femto-second laser according to claim 1, feature exist In：G.652 single mode optical fiber, incident optical (1) and the output optical fiber (3) length can be used in incident optical (1), the output optical fiber (3) For 20~40cm.

3. a kind of optical fiber air ring cavity temperature sensor based on femto-second laser according to claim 1, feature exist In：G.652 single mode optical fiber can be used in optical fiber used in air ring cavity configuration (2), and length is 50um~100um, air ring cavity The ring cavity exradius of structure (2) is 4um~7um, and inner circle radius is 2um~5um.