CN112146853A - Narrow linewidth laser frequency drift detection device based on double-optical-fiber interferometer - Google Patents
Narrow linewidth laser frequency drift detection device based on double-optical-fiber interferometer Download PDFInfo
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Abstract
The invention discloses a narrow linewidth laser frequency drift detection device based on a double-fiber interferometer, which mainly comprises a 1 multiplied by 2 fiber splitter, 2 fiber interferometers and a phase drift detection circuit. The 2 fiber interferometers are michelson fiber interferometers and/or mach-zehnder fiber interferometers. The measuring fibers of the 2 fiber interferometers have different temperature delay coefficients. The double interferometer demodulates and measures the phase drift generated by the frequency drift of the laser in the optical fiber and the phase drift generated by the temperature change by obtaining two phase drift detection values. The invention can realize high-precision laser frequency drift detection in a common working environment, thereby improving the frequency stability of the commercial narrow linewidth laser by one to two orders of magnitude or providing a reference basis for a fiber interferometer to correct system errors caused by laser frequency drift, and meeting the requirements of compact packaging volume and low cost.
Description
Technical Field
The invention relates to the technical field of lasers, in particular to a narrow linewidth laser frequency drift detection device based on a double-fiber interferometer.
Background
The narrow linewidth laser has good coherence performance and is widely applied to the technical fields of laser radars, optical instruments and various optical fiber sensing. The existing narrow linewidth laser, such as a narrow linewidth optical fiber laser, a narrow linewidth semiconductor laser and the like, generally adopts a compact F-P interferometer for frequency stabilization, and because the cavity length of an F-P cavity is too short and the influence of factors such as thermodynamic noise, environmental vibration noise and the like exists, the laser frequency stability of the narrow linewidth laser in a common environment can only be controlled at the magnitude of 10 MHz. And the technical means such as gas molecule saturated absorption and super stable cavity are not favorable for compact structure design, and have high construction and use cost and difficult popularization and application. However, in some precision measurement fields, the frequency drift of the narrow linewidth laser becomes a main source of system detection error, and for this reason, the frequency drift of the narrow linewidth laser needs to be detected, so as to compensate the narrow linewidth laser by using the frequency drift detection result, or to correct the system detection error by using the frequency drift detection result.
Disclosure of Invention
The invention aims to solve the problem of insufficient frequency drift stability of the existing narrow linewidth laser and provides a narrow linewidth laser frequency drift detection device based on a double-fiber interferometer.
In order to solve the problems, the invention is realized by the following technical scheme:
the narrow linewidth laser frequency drift detection device based on the double-optical fiber interferometer mainly comprises a 1 multiplied by 2 optical fiber splitter, 2 optical fiber interferometers and a phase drift detection circuit; the 2 optical fiber interferometers are Michelson optical fiber interferometers and/or Mach-Zehnder optical fiber interferometers; wherein: each Michelson optical fiber interferometer consists of an A-type optical fiber coupler, a measuring optical fiber and 2 Faraday magnetic rotating reflectors; the left side of the A-type fiber coupler comprises at least 2 ports, wherein one port forms the input end of the fiber interferometer, and the other port forms the output end of the fiber interferometer; the right side of the A-type optical fiber coupler comprises at least 2 ports, wherein one port is connected with one Faraday magnetic rotation reflector through a measuring optical fiber, and the other port is directly connected with the other Faraday magnetic rotation reflector; each Mach-Zehnder optical fiber interferometer consists of a B-type optical fiber coupler, a measuring optical fiber and a C-type optical fiber coupler; the left side of the type-B fiber coupler comprises at least 1 port, wherein one port forms the input end of the fiber interferometer; the right side of the type-C fiber coupler comprises at least 1 port, wherein one port forms the output end of the fiber interferometer; the right side of the type B fiber coupler includes at least 2 ports; the left side of the type C fiber coupler includes at least 2 ports; one port on the right side of the B-type optical fiber coupler is connected with one port on the left side of the C-type optical fiber coupler through a measuring optical fiber; the other port on the right side of the B-type optical fiber coupler is directly connected with the other port on the left side of the C-type optical fiber coupler; the measuring optical fibers of the 2 optical fiber interferometers have different temperature delay coefficients; the input end of the 1 multiplied by 2 optical fiber branching unit forms the input end of the frequency drift detection device of the narrow linewidth laser and inputs the monitoring laser of the narrow linewidth laser; 2 output ends of the 1 multiplied by 2 optical fiber branching unit are respectively connected with the input end of an optical fiber interferometer, and the output ends of the 2 optical fiber interferometers are connected with the input end of the phase drift detection circuit; the output end of the phase drift detection circuit forms the output end of the narrow linewidth laser frequency drift detection device and outputs the measurement optical fiber phase drift amount and/or the laser frequency drift amount generated by the laser frequency drift.
When 2 fiber interferometers are all michelson fiber interferometers:
measuring optical fiber L output by phase drift detection circuit1Phase drift amount N generated by frequency drift of internal laser1Comprises the following steps:
phase drift detection circuit outputOf the measuring fiber L2Phase drift amount N generated by frequency drift of internal laser2Comprises the following steps:
the laser frequency drift amount delta f output by the phase drift detection circuit is as follows:
in the formula, A represents the ratio of the temperature delay coefficients of the measuring fibers of the first Michelson fiber interferometer and the second Michelson fiber interferometer, and A is not equal to 1; l is1Indicating the length, L, of the measuring fiber of the first Michelson fiber interferometer2Representing the length of the measuring fiber of the second Michelson fiber interferometer; n is a radical ofL1Representing the fibre phase drift value, N, of the first Michelson fibre interferometerL2Respectively representing the fiber phase drift detection values of a second Michelson fiber interferometer; c is the vacuum light speed; n is the refractive index of the fiber.
When 2 fiber interferometers are all mach-zehnder fiber interferometers:
measuring optical fiber L output by phase drift detection circuit1Phase drift amount N generated by frequency drift of internal laser1Comprises the following steps:
measuring optical fiber L output by phase drift detection circuit2Phase drift amount N generated by frequency drift of internal laser2Comprises the following steps:
the laser frequency drift amount delta f output by the phase drift detection circuit is as follows:
in the formula, A represents the ratio of the temperature delay coefficients of the measuring optical fibers of the first Mach-Zehnder optical fiber interferometer and the second Mach-Zehnder optical fiber interferometer, and A is not equal to 1; l is1Representing the length, L, of the measuring fibre of the first Mach-Zehnder fibre-optic interferometer2Representing the length of the measuring fiber of the second Mach-Zehnder fiber optic interferometer; n is a radical ofL1Representing the measured value of the fiber phase shift, N, of the first Mach-Zehnder fiber interferometerL2Respectively representing the fiber phase drift detection values of the second Mach-Zehnder fiber optic interferometers; c is the vacuum light speed; n is the refractive index of the fiber.
When the 2 fiber interferometers are michelson fiber interferometers and mach-zehnder fiber interferometers:
measuring optical fiber L of Mach-Zehnder optical fiber interferometer output by phase drift detection circuit1Phase drift amount N generated by frequency drift of internal laser1Comprises the following steps:
measuring optical fiber L of Michelson optical fiber interferometer output by phase drift detection circuit2Phase drift amount N generated by frequency drift of internal laser2Comprises the following steps:
the laser frequency drift amount delta f output by the phase drift detection circuit is as follows:
wherein A represents Mach-ZehnderThe ratio of the temperature delay coefficients of the measurement optical fibers of the optical fiber interferometer and the Michelson optical fiber interferometer is A not equal to 1; l is1Length, L, of measuring fiber of Mach-Zehnder fiber optic interferometer2The length of a measuring optical fiber of the Michelson optical fiber interferometer is represented; n is a radical ofL1Representing the fiber phase drift detection value, N, of a Mach-Zehnder fiber optic interferometerL2Respectively representing the fiber phase drift detection values of the Michelson fiber optic interferometer; c is the vacuum light speed; n is the refractive index of the fiber.
In the above scheme, the type a fiber coupler is a 2 × 2 fiber coupler or a 3 × 3 fiber coupler.
In the scheme, the B-type optical fiber coupler of the Mach-Zehnder optical fiber interferometer is a 1 × 2 optical fiber coupler, a 2 × 2 optical fiber coupler or a 3 × 3 optical fiber coupler; the C-type optical fiber coupler is a 2 × 1 optical fiber coupler, a 2 × 2 optical fiber coupler or a 3 × 3 optical fiber coupler.
Compared with the prior art, the double-fiber interferometer-based narrow linewidth laser frequency drift detection device can realize high-precision laser frequency drift detection in a common working environment, so that the frequency stability of a commercial narrow linewidth laser can be improved by one to two orders of magnitude or a reference basis is provided for a fiber interferometer to correct system errors caused by laser frequency drift, and the requirements of compact packaging volume and low cost can be met.
Drawings
Fig. 1 is a schematic diagram of a narrow linewidth laser frequency drift detection device based on a double-fiber interferometer (double michelson fiber interferometer).
Fig. 2 is a schematic diagram of the arm length of the michelson fiber optic interferometer of fig. 1.
Fig. 3 is a schematic diagram of another dual-fiber interferometer (dual mach-zehnder fiber interferometer) based narrow linewidth laser frequency drift detection device.
FIG. 4 is a schematic diagram of the arm length of the Mach-Zehnder fiber optic interferometer of FIG. 3.
Fig. 5 is a schematic diagram of another apparatus for detecting frequency drift of a narrow-linewidth laser based on a dual-fiber interferometer (michelson fiber interferometer and mach-zehnder fiber interferometer).
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to specific examples.
The narrow linewidth laser frequency drift detection device based on the double-optical-fiber interferometer comprises 1 × 2 optical fiber branching unit, 2 optical fiber interferometers and a phase drift detection circuit, wherein two optical fibers with different temperature delay coefficients (the unit is ps/km/k, k is the degree of kelvin, and 1k is 1 ℃) are respectively used on measuring arms of the two optical fiber interferometers. The narrow linewidth laser emits a beam of monitoring laser signal to access a 1 x 2 optical fiber branching unit, two paths of narrow linewidth laser signals output by the 1 x 2 optical fiber branching unit enter 2 optical fiber interferometers, the 2 optical fiber interferometers respectively carry out optical fiber phase drift detection, and the optical fiber phase drift amount and/or the laser frequency drift amount generated by the frequency drift of the narrow linewidth laser are solved according to the phase drift detection results of the two optical fiber interferometers, and the measured optical fiber phase drift amount and/or the laser frequency drift amount generated by the frequency drift of the laser can be used for laser frequency drift feedback compensation control on one hand and can be used for correcting system errors generated by the frequency drift of the laser by the optical fiber sensor on the other hand.
Example 1:
referring to fig. 1, a dual-fiber interferometer-based narrow-linewidth laser frequency drift detection device mainly comprises a 1 × 2 fiber splitter, 2 fiber interferometers and a phase drift detection circuit. The input end of the 1 x 2 optical fiber splitter forms the input end of the narrow-linewidth laser frequency drift detection device and inputs the monitoring laser of the narrow-linewidth laser. 2 output ends of the 1 multiplied by 2 optical fiber branching units are respectively connected with the input end of one optical fiber interferometer, and the output ends of the 2 optical fiber interferometers are connected with the input end of the phase drift detection circuit. The output end of the phase drift detection circuit forms the output end of the narrow linewidth laser frequency drift detection device, and the phase drift detection circuit outputs the measurement optical fiber phase drift amount and/or the laser frequency drift amount generated by the laser frequency drift. In this embodiment, the optical power output from the 2 splitting ends of the 1 × 2 optical splitter is equal.
The 2 optical fiber interferometers are all Michelson optical fiber interferometers. Each Michelson fiber interferometer consists of an A-type fiber coupler, a measuring fiber and 2 Faraday magnetic rotating reflectors. The left side of the type a fiber coupler includes at least 2 ports, one of which forms the input end of the fiber interferometer and the other of which forms the output end of the fiber interferometer. The right side of the A-type optical fiber coupler comprises at least 2 ports, wherein one port is connected with one Faraday magnetic rotation reflector through a measuring optical fiber to form a measuring arm of the optical fiber interferometer, and the other port is directly connected with the other Faraday magnetic rotation reflector to form a reference arm of the optical fiber interferometer. The measuring fibers of the 2 michelson fiber interferometers have different temperature delay coefficients. In this embodiment, the measuring fiber of one michelson fiber interferometer is a common single-mode fiber, and the measuring fiber of the other michelson fiber interferometer is a fiber having a temperature drift coefficient different from that of the common single-mode fiber.
The A-type fiber coupler of the Michelson fiber interferometer can be a 2X 2 fiber coupler or a 3X 3 fiber coupler. When the type a fiber coupler is a 2 × 2 fiber coupler, 1 output end of each michelson fiber interferometer is connected to 1 photodetector of the phase drift detection circuit. When the type a fiber coupler is a 3 × 3 fiber coupler, 2 output ends of each michelson fiber interferometer are connected to 2 photodetectors of the phase drift detection circuit.
For each Michelson fiber interferometer, the difference in arm length between the measurement arm and the reference arm is equal to the length of the measurement fiber. The length of the measuring optical fiber of the first Michelson optical fiber interferometer is L1And the length of the measuring optical fiber of the second Michelson optical fiber interferometer is L2. As shown in fig. 2.
Suppose L1And L2All of which are constant, i.e. no variation in fibre delay, narrow linewidth laser from frequency f1Change to frequency f2The number of coherence cycles generated is:
wherein λ is1Is the laser frequency f1Corresponding to the wavelength of the laser, λ2Is the laser frequency f2Corresponding to the wavelength of the laser, N1And N2Is a rational number containing a fractional part, n is the refractive index of the optical fiber, c is the vacuum speed of light, and c ═ λ1f1＝λ2f2。
Assuming that the working frequency of the laser is constant, i.e. no frequency drift is generated, the measuring fiber length is affected by temperature to generate phase drift, and the measuring fiber length L1To L'1Measuring the length L of the optical fiber2To L'2The number of coherence cycles generated is:
wherein N is3And N4Is a rational number that contains a fractional part.
Regardless of the effect of vibration on the fiber delay, the phase shift detected by the fiber interferometer results in two phase shifts: phase drift generated by the change of the optical fiber delay and phase drift generated by the laser frequency drift. Namely:
wherein N isL1And NL2Is a rational number that contains a fractional part.
The temperature delay coefficient of a particular fiber is a known quantity that can be accurately measured, assuming that the fiber L is measured2And a measuring fiber L1The ratio of the temperature delay coefficients is A, and the two optical fibers have the same temperature change under the same environment, so that the temperature delay coefficients are:
the formula (1) and (2) can be used for obtaining:
the formula (3), (4) and (7) can be used to obtain:
from the formulae (5), (6), (8) and (9)
Measuring fiber L1The phase shift amount generated by the frequency shift of the internal laser is as follows:
or measuring optical fibre L2The phase shift amount generated by the frequency shift of the internal laser is as follows:
wherein the length L of the optical fiber is measured1And L2For a known quantity, A is the ratio of the temperature delay coefficients of the two fibers, and A ≠ 1, also a known quantity, NL1And NL2For detecting the value of the fiber-optic interferometer, it can pass through a dual interferometerAnd (3) solving the phase drift amount generated by the laser frequency drift by using the measuring optical fibers with different temperature delay coefficients.
The phase drift detection circuit utilizes the demodulated phase drift quantity N1Or N2The laser frequency drift amount Δ f can be calculated as:
when the measured fiber phase drift amount generated by the laser frequency drift detected by the phase drift detection circuit and/or the laser frequency drift amount is used for correcting the system error generated by the laser frequency drift by the fiber sensor, the output end of the phase drift detection circuit is connected with the fiber sensor signal processing module. When the measured fiber phase drift amount and/or the laser frequency drift amount generated by the laser frequency drift detected by the phase drift detection circuit is used for the laser frequency drift feedback compensation control, the signal output end of the phase drift detection circuit is connected to the laser frequency drift feedback compensation device, and the narrow linewidth laser feeds back and controls the frequency drift adjusting device according to the result detected by the phase drift detection circuit, so that the frequency drift of the narrow linewidth laser is at the lowest level.
Example 2:
referring to fig. 3, a dual-fiber interferometer-based narrow-linewidth laser frequency drift detection apparatus is mainly composed of a 1 × 2 fiber splitter, 2 fiber interferometers and a phase drift detection circuit. The input end of the 1 x 2 optical fiber splitter forms the input end of the narrow-linewidth laser frequency drift detection device and inputs the monitoring laser of the narrow-linewidth laser. 2 output ends of the 1 multiplied by 2 optical fiber branching units are respectively connected with the input end of one optical fiber interferometer, and the output ends of the 2 optical fiber interferometers are connected with the input end of the phase drift detection circuit. The output end of the phase drift detection circuit forms the output end of the narrow linewidth laser frequency drift detection device, and the phase drift detection circuit outputs the measurement optical fiber phase drift amount and/or the laser frequency drift amount generated by the laser frequency drift. In this embodiment, the optical power output from the 2 splitting ends of the 1 × 2 optical splitter is equal.
The 2 optical fiber interferometers are all Mach-Zehnder optical fiber interferometers. Each Mach-Zehnder optical fiber interferometer consists of a B-type optical fiber coupler, a measuring optical fiber and a C-type optical fiber coupler. The left side of the type B fiber coupler includes at least 1 port, one of which forms the input of the fiber optic interferometer. The right side of the type C fiber coupler includes at least 1 port, one of which forms the output of the fiber optic interferometer. The right side of the type B fiber coupler includes at least 2 ports. The left side of the type C fiber coupler includes at least 2 ports. One port on the right side of the B-type fiber coupler is connected to one port on the left side of the C-type fiber coupler via a measurement fiber, forming a measurement arm of the Mach-Zehnder fiber optic interferometer. The other port on the right side of the B-type optical fiber coupler is directly connected with the other port on the left side of the C-type optical fiber coupler to form a reference arm of the Mach-Zehnder optical fiber interferometer. The measuring fibers of the 2 mach-zehnder fiber interferometers have different temperature delay coefficients. In this embodiment, the measuring fiber of one mach-zehnder fiber interferometer is a normal single-mode fiber, and the measuring fiber of the other mach-zehnder fiber interferometer is a fiber having a temperature drift coefficient different from that of the normal single-mode fiber.
The B-type optical fiber coupler of the Mach-Zehnder optical fiber interferometer is a 1 x 2 optical fiber coupler, a 2 x 2 optical fiber coupler or a 3 x 3 optical fiber coupler. The C-type optical fiber coupler of the Mach-Zehnder optical fiber interferometer is a 2 x 1 optical fiber coupler, a 2 x 2 optical fiber coupler or a 3 x 3 optical fiber coupler. When the C-type optical fiber coupler of the Mach-Zehnder optical fiber interferometer is a 2 x 2 or 2 x 1 optical fiber coupler, 1 output end of each Mach-Zehnder optical fiber interferometer is connected with 1 photoelectric detector of the phase drift detection circuit. When the type-C optical fiber coupler of the optical fiber coupler at the output end of the optical fiber interferometer is a 3 x 3 optical fiber coupler, 2 output ends of each Michelson optical fiber interferometer are connected with 2 photodetectors of the phase drift detection circuit.
For each mach-zehnder fiber optic interferometer, the difference in arm length between the measurement arm and the reference arm is equal to the length of the measurement fiber. First Mach-Zehnder fiber optic interferometerMeasuring optical fiber length of L1The measuring fiber length of the second Mach-Zehnder fiber interferometer is L2. As shown in fig. 4.
Suppose L1And L2All of which are constant, i.e. no variation in fibre delay, narrow linewidth laser from frequency f1Change to frequency f2The number of coherence cycles generated is:
wherein λ is1Is the laser frequency f1Corresponding to the wavelength of the laser, λ2Is the laser frequency f2Corresponding to the wavelength of the laser, N1And N2Is a rational number containing a fractional part, n is the refractive index of the optical fiber, c is the vacuum speed of light, and c ═ λ1f1＝λ2f2。
Assuming that the working frequency of the laser is constant, i.e. no frequency drift is generated, the measuring fiber length is affected by temperature to generate phase drift, and the measuring fiber length L1To L'1Measuring the length L of the optical fiber2To L'2The number of coherence cycles generated is:
wherein N is3And N4Is a rational number that contains a fractional part.
Regardless of the effect of vibration on the fiber delay, the phase shift detected by the fiber interferometer results in two phase shifts: phase drift generated by the change of the optical fiber delay and phase drift generated by the laser frequency drift. Namely:
wherein N isL1And NL2Is a rational number that contains a fractional part.
The temperature delay coefficient of a particular fiber is a known quantity that can be accurately measured, assuming that the fiber L is measured2And a measuring fiber L1The ratio of the temperature delay coefficients is A, and the two optical fibers have the same temperature change under the same environment, so that the temperature delay coefficients are:
the formula (13) and (14) can be used for obtaining:
the following formulae (15), (16) and (19) can be obtained:
from the formulae (17), (18), (20), (21)
Measuring fiber L1The phase shift amount generated by the frequency shift of the internal laser is as follows:
or measuring optical fibre L2The phase shift amount generated by the frequency shift of the internal laser is as follows:
wherein the length L of the optical fiber is measured1And L2For a known quantity, A is the ratio of the temperature delay coefficients of the two fibers, and A ≠ 1, also a known quantity, NL1And NL2The phase drift amount generated by laser frequency drift can be obtained by using measuring optical fibers with different temperature delay coefficients through double interferometers.
When the 2 optical fiber interferometers are Mach-Zehnder optical fiber interferometers, the phase drift detection circuit utilizes the demodulated phase drift quantity N1Or N2The laser frequency drift amount Δ f can be calculated as:
when the measured fiber phase drift amount generated by the laser frequency drift detected by the phase drift detection circuit and/or the laser frequency drift amount is used for correcting the system error generated by the laser frequency drift by the fiber sensor, the output end of the phase drift detection circuit is connected with the fiber sensor signal processing module. When the measured fiber phase drift amount and/or the laser frequency drift amount generated by the laser frequency drift detected by the phase drift detection circuit is used for the laser frequency drift feedback compensation control, the signal output end of the phase drift detection circuit is connected to the laser frequency drift feedback compensation device, and the narrow linewidth laser feeds back and controls the frequency drift adjusting device according to the result detected by the phase drift detection circuit, so that the frequency drift of the narrow linewidth laser is at the lowest level.
Example 3:
referring to fig. 5, another apparatus for detecting frequency drift of a narrow-linewidth laser based on a dual-fiber interferometer mainly comprises a 1 × 2 fiber splitter, 2 fiber interferometers and a phase drift detection circuit. The input end of the 1 x 2 optical fiber splitter forms the input end of the narrow-linewidth laser frequency drift detection device and inputs the monitoring laser of the narrow-linewidth laser. 2 output ends of the 1 multiplied by 2 optical fiber branching units are respectively connected with the input end of one optical fiber interferometer, and the output ends of the 2 optical fiber interferometers are connected with the input end of the phase drift detection circuit. The output end of the phase drift detection circuit forms the output end of the narrow linewidth laser frequency drift detection device, and the phase drift detection circuit outputs the measurement optical fiber phase drift amount and/or the laser frequency drift amount generated by the laser frequency drift. In this embodiment, the optical power output from the 2 splitting ends of the 1 × 2 optical splitter is equal.
One of the 2 fiber-optic interferometers is a michelson fiber-optic interferometer, and the other is a mach-zehnder fiber-optic interferometer.
The Michelson fiber interferometer consists of an A-type fiber coupler, a measuring fiber and 2 Faraday magnetic rotating reflectors. The left side of the type a fiber coupler includes at least 2 ports, one of which forms the input end of the fiber interferometer and the other of which forms the output end of the fiber interferometer. The right side of the A-type optical fiber coupler comprises at least 2 ports, wherein one port is connected with one Faraday magnetic rotation reflector through a measuring optical fiber to form a measuring arm of the optical fiber interferometer, and the other port is directly connected with the other Faraday magnetic rotation reflector to form a reference arm of the optical fiber interferometer.
The A-type fiber coupler of the Michelson fiber interferometer can be a 2X 2 fiber coupler or a 3X 3 fiber coupler. When the a-type fiber coupler of the michelson fiber optic interferometer is a 2 × 2 fiber coupler, 1 output end of each michelson fiber optic interferometer is connected to 1 photodetector of the phase drift detection circuit. When the type a fiber coupler of the michelson fiber optic interferometer is a 3 × 3 fiber coupler, 2 output ends of each michelson fiber optic interferometer are connected to 2 photodetectors of the phase drift detection circuit.
The Mach-Zehnder optical fiber interferometer consists of a B-type optical fiber coupler, a measuring optical fiber and a C-type optical fiber coupler. The left side of the type B fiber coupler includes at least 1 port, one of which forms the input of the fiber optic interferometer. The right side of the type C fiber coupler includes at least 1 port, one of which forms the output of the fiber optic interferometer. The right side of the type B fiber coupler includes at least 2 ports. The left side of the type C fiber coupler includes at least 2 ports. One port on the right side of the B-type fiber coupler is connected to one port on the left side of the C-type fiber coupler via a measurement fiber, forming a measurement arm of the Mach-Zehnder fiber optic interferometer. The other port on the right side of the B-type optical fiber coupler is directly connected with the other port on the left side of the C-type optical fiber coupler to form a reference arm of the Mach-Zehnder optical fiber interferometer.
The B-type optical fiber coupler of the Mach-Zehnder optical fiber interferometer is a 1 x 2 optical fiber coupler, a 2 x 2 optical fiber coupler or a 3 x 3 optical fiber coupler. The C-type optical fiber coupler of the Mach-Zehnder optical fiber interferometer is a 2 x 1 optical fiber coupler, a 2 x 2 optical fiber coupler or a 3 x 3 optical fiber coupler. When the C-type optical fiber coupler of the Mach-Zehnder optical fiber interferometer is a 2 x 2 or 2 x 1 optical fiber coupler, 1 output end of each Mach-Zehnder optical fiber interferometer is connected with 1 photoelectric detector of the phase drift detection circuit. When the type-C optical fiber coupler of the optical fiber coupler at the output end of the optical fiber interferometer is a 3 x 3 optical fiber coupler, 2 output ends of each Michelson optical fiber interferometer are connected with 2 photodetectors of the phase drift detection circuit.
The measuring fiber of the Michelson fiber optic interferometer and the measuring fiber of the Mach-Zehnder fiber optic interferometer have different temperature delay coefficients. In this embodiment, the measuring fiber of one michelson fiber interferometer is a common single-mode fiber, and the measuring fiber of the other michelson fiber interferometer is a fiber having a temperature drift coefficient different from that of the common single-mode fiber.
For Mach-Zehnder and Michelson fiber interferometers, the difference in arm length between their measurement and reference arms is equal to the length of their measurement fibers. The Mach-Zehnder fiber interferometer has a measuring fiber length L1The length of the measuring optical fiber of the Michelson optical fiber interferometer is L2。
Suppose L1And L2All of which are constant, i.e. no variation in fibre delay, narrow linewidth laser from frequency f1Change to frequency f2The number of coherence cycles generated is:
wherein λ is1Is the laser frequency f1Corresponding to the wavelength of the laser, λ2Is the laser frequency f2Corresponding to the wavelength of the laser, N1And N2Is a rational number containing a fractional part, n is the refractive index of the optical fiber, c is the vacuum speed of light, and c ═ λ1f1＝λ2f2。
Assuming that the working frequency of the laser is constant, i.e. no frequency drift is generated, the measuring fiber length is affected by temperature to generate phase drift, and the measuring fiber length L1To L'1Measuring the length L of the optical fiber2To L'2The number of coherence cycles generated is:
wherein N is3And N4Is a rational number that contains a fractional part.
Regardless of the effect of vibration on the fiber delay, the phase shift detected by the fiber interferometer results in two phase shifts: phase drift generated by the change of the optical fiber delay and phase drift generated by the laser frequency drift. Namely:
the temperature delay coefficient of a particular fiber is a known quantity that can be accurately measured, assuming that the fiber L is measured2And a measuring fiber L1The ratio of the temperature delay coefficients is A, and the two optical fibers have the same temperature change under the same environment, so that the temperature delay coefficients are:
the following formulae (25) and (26) can be obtained:
from the formulae (27), (28), (31):
from the formulae (29), (30), (32), (33)
Measuring fiber L1The amount of phase shift generated by frequency shift of the internal laser is
Or measuring optical fibre L2The amount of phase shift generated by frequency shift of the internal laser is
Wherein the length L of the optical fiber is measured1And L2For a known quantity, A is the ratio of the temperature delay coefficients of the two fibers, and A ≠ 1, also a known quantity, NL1And NL2Is a detection value of the fiber interferometer, so that the fiber interferometer can be switched onThe double interferometers use measuring optical fibers with different temperature delay coefficients to obtain the laser frequency drift amount.
The phase drift detection circuit utilizes the demodulated phase drift quantity N1Or N2The laser frequency drift amount Δ f can be calculated as:
when the measured fiber phase drift amount generated by the laser frequency drift detected by the phase drift detection circuit and/or the laser frequency drift amount is used for correcting the system error generated by the laser frequency drift by the fiber sensor, the output end of the phase drift detection circuit is connected with the fiber sensor signal processing module. When the measured fiber phase drift amount and/or the laser frequency drift amount generated by the laser frequency drift detected by the phase drift detection circuit is used for the laser frequency drift feedback compensation control, the signal output end of the phase drift detection circuit is connected to the laser frequency drift feedback compensation device, and the narrow linewidth laser feeds back and controls the frequency drift adjusting device according to the result detected by the phase drift detection circuit, so that the frequency drift of the narrow linewidth laser is at the lowest level.
It should be noted that, although the above-mentioned embodiments of the present invention are illustrative, the present invention is not limited thereto, and thus the present invention is not limited to the above-mentioned embodiments. Other embodiments, which can be made by those skilled in the art in light of the teachings of the present invention, are considered to be within the scope of the present invention without departing from its principles.
Claims (6)
1. The narrow linewidth laser frequency drift detection device based on the double-optical fiber interferometer is characterized by mainly comprising a 1 multiplied by 2 optical fiber splitter, 2 optical fiber interferometers and a phase drift detection circuit;
the 2 optical fiber interferometers are Michelson optical fiber interferometers and/or Mach-Zehnder optical fiber interferometers; wherein:
each Michelson optical fiber interferometer consists of an A-type optical fiber coupler, a measuring optical fiber and 2 Faraday magnetic rotating reflectors; the left side of the A-type fiber coupler comprises at least 2 ports, wherein one port forms the input end of the fiber interferometer, and the other port forms the output end of the fiber interferometer; the right side of the A-type optical fiber coupler comprises at least 2 ports, wherein one port is connected with one Faraday magnetic rotation reflector through a measuring optical fiber, and the other port is directly connected with the other Faraday magnetic rotation reflector;
each Mach-Zehnder optical fiber interferometer consists of a B-type optical fiber coupler, a measuring optical fiber and a C-type optical fiber coupler; the left side of the type-B fiber coupler comprises at least 1 port, wherein one port forms the input end of the fiber interferometer; the right side of the type-C fiber coupler comprises at least 1 port, wherein one port forms the output end of the fiber interferometer; the right side of the type B fiber coupler includes at least 2 ports; the left side of the type C fiber coupler includes at least 2 ports; one port on the right side of the B-type optical fiber coupler is connected with one port on the left side of the C-type optical fiber coupler through a measuring optical fiber; the other port on the right side of the B-type optical fiber coupler is directly connected with the other port on the left side of the C-type optical fiber coupler;
the measuring optical fibers of the 2 optical fiber interferometers have different temperature delay coefficients;
the input end of the 1 multiplied by 2 optical fiber branching unit forms the input end of the frequency drift detection device of the narrow linewidth laser and inputs the monitoring laser of the narrow linewidth laser; 2 output ends of the 1 multiplied by 2 optical fiber branching unit are respectively connected with the input end of an optical fiber interferometer, and the output ends of the 2 optical fiber interferometers are connected with the input end of the phase drift detection circuit; the output end of the phase drift detection circuit forms the output end of the narrow linewidth laser frequency drift detection device and outputs the measurement optical fiber phase drift amount and/or the laser frequency drift amount generated by the laser frequency drift.
2. The apparatus for detecting frequency drift of a narrow-linewidth laser based on a dual-fiber interferometer according to claim 1, wherein when the 2 fiber interferometers are all michelson fiber interferometers:
measuring optical fiber L output by phase drift detection circuit1Phase drift amount N generated by frequency drift of internal laser1Comprises the following steps:
measuring optical fiber L output by phase drift detection circuit2Phase drift amount N generated by frequency drift of internal laser2Comprises the following steps:
the laser frequency drift amount delta f output by the phase drift detection circuit is as follows:
in the formula, A represents the ratio of the temperature delay coefficients of the measuring fibers of the first Michelson fiber interferometer and the second Michelson fiber interferometer, and A is not equal to 1; l is1Indicating the length, L, of the measuring fiber of the first Michelson fiber interferometer2Representing the length of the measuring fiber of the second Michelson fiber interferometer; n is a radical ofL1Representing the fibre phase drift value, N, of the first Michelson fibre interferometerL2Respectively representing the fiber phase drift detection values of a second Michelson fiber interferometer; c is the vacuum light speed; n is the refractive index of the fiber.
3. The dual-fiber interferometer-based narrow-linewidth laser frequency drift detection device of claim 1, wherein when 2 fiber interferometers are all mach-zehnder fiber interferometers:
measuring optical fiber L output by phase drift detection circuit1Amount of phase shift due to frequency drift of internal laserN1Comprises the following steps:
measuring optical fiber L output by phase drift detection circuit2Phase drift amount N generated by frequency drift of internal laser2Comprises the following steps:
the laser frequency drift amount delta f output by the phase drift detection circuit is as follows:
in the formula, A represents the ratio of the temperature delay coefficients of the measuring optical fibers of the first Mach-Zehnder optical fiber interferometer and the second Mach-Zehnder optical fiber interferometer, and A is not equal to 1; l is1Representing the length, L, of the measuring fibre of the first Mach-Zehnder fibre-optic interferometer2Representing the length of the measuring fiber of the second Mach-Zehnder fiber optic interferometer; n is a radical ofL1Representing the measured value of the fiber phase shift, N, of the first Mach-Zehnder fiber interferometerL2Respectively representing the fiber phase drift detection values of the second Mach-Zehnder fiber optic interferometers; c is the vacuum light speed; n is the refractive index of the fiber.
4. The dual-fiber interferometer-based narrow-linewidth laser frequency drift detection device of claim 1, wherein when the 2 fiber interferometers are michelson fiber interferometers and mach-zehnder fiber interferometers:
measuring optical fiber L of Mach-Zehnder optical fiber interferometer output by phase drift detection circuit1Phase drift amount N generated by frequency drift of internal laser1Comprises the following steps:
measuring optical fiber L of Michelson optical fiber interferometer output by phase drift detection circuit2Phase drift amount N generated by frequency drift of internal laser2Comprises the following steps:
the laser frequency drift amount delta f output by the phase drift detection circuit is as follows:
in the formula, A represents the ratio of the temperature delay coefficient of a measuring optical fiber of a Mach-Zehnder optical fiber interferometer and a Michelson optical fiber interferometer, and A is not equal to 1; l is1Length, L, of measuring fiber of Mach-Zehnder fiber optic interferometer2The length of a measuring optical fiber of the Michelson optical fiber interferometer is represented; n is a radical ofL1Representing the fiber phase drift detection value, N, of a Mach-Zehnder fiber optic interferometerL2Respectively representing the fiber phase drift detection values of the Michelson fiber optic interferometer; c is the vacuum light speed; n is the refractive index of the fiber.
5. The apparatus of claim 1, wherein the type-A fiber coupler is a 2 x 2 fiber coupler or a 3 x 3 fiber coupler.
6. The dual-fiber interferometer-based narrow-linewidth laser frequency drift detection device of claim 1, wherein the B-type fiber coupler of the mach-zehnder fiber interferometer is a 1 x 2 fiber coupler, a 2 x 2 fiber coupler or a 3 x 3 fiber coupler; the C-type optical fiber coupler is a 2 × 1 optical fiber coupler, a 2 × 2 optical fiber coupler or a 3 × 3 optical fiber coupler.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113312805A (en) * | 2021-07-29 | 2021-08-27 | 中国人民解放军国防科技大学 | Method for evaluating melting point quality of high-power fiber laser |
| CN113639847A (en) * | 2021-08-06 | 2021-11-12 | 天津大学 | Pulse modulation and demodulation module and distributed optical fiber vibration sensing positioning method |
| CN113746545A (en) * | 2021-09-18 | 2021-12-03 | 中国电子科技集团公司第三十四研究所 | Calibration device for optical fiber phase-stabilized transmission equipment |
| US11575436B1 (en) * | 2022-01-20 | 2023-02-07 | Rohde & Schwarz Gmbh & Co. Kg | System for correcting phase noise and/or drift in an optical fiber for a network analyzer |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113312805A (en) * | 2021-07-29 | 2021-08-27 | 中国人民解放军国防科技大学 | Method for evaluating melting point quality of high-power fiber laser |
| CN113312805B (en) * | 2021-07-29 | 2021-10-26 | 中国人民解放军国防科技大学 | Method for evaluating melting point quality of high-power fiber laser |
| CN113639847A (en) * | 2021-08-06 | 2021-11-12 | 天津大学 | Pulse modulation and demodulation module and distributed optical fiber vibration sensing positioning method |
| CN113746545A (en) * | 2021-09-18 | 2021-12-03 | 中国电子科技集团公司第三十四研究所 | Calibration device for optical fiber phase-stabilized transmission equipment |
| CN113746545B (en) * | 2021-09-18 | 2023-06-20 | 中国电子科技集团公司第三十四研究所 | Calibrating device for optical fiber stable phase transmission equipment |
| US11575436B1 (en) * | 2022-01-20 | 2023-02-07 | Rohde & Schwarz Gmbh & Co. Kg | System for correcting phase noise and/or drift in an optical fiber for a network analyzer |
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