CN-121983839-A - Tunable single longitudinal mode erbium-doped fiber laser based on double filters

CN121983839ACN 121983839 ACN121983839 ACN 121983839ACN-121983839-A

Abstract

The invention discloses a tunable single longitudinal mode erbium-doped fiber laser based on a double filter, which comprises 976 nanometer pump source, 976 nanometer/1550 nanometer wavelength division multiplexer, erbium-doped fiber, fiber isolator, 3dB fiber coupler, uniform fiber grating I, uniform fiber grating II, 3X 3 fiber coupler I, 3X 3 fiber coupler II and 90:10 fiber coupler, wherein the double filter used in the invention can effectively expand the longitudinal mode interval of the laser and realize ultra-narrow band filtering effect, and has outstanding single longitudinal mode selection capability and linewidth narrowing function; the fiber bragg grating is packaged on polytetrafluoroethylene materials with high temperature sensitivity, and the ultra-narrow band filtering function of the series double filters is combined, so that the high-stability operation of the tunable narrow-linewidth single longitudinal mode laser can be realized.

Inventors

LIU YUN
DUAN TENGFEI
LI RUI
XING JUNHONG
LI HEQUN
WANG XIAN

Assignees

西安理工大学

Dates

Publication Date: 20260505
Application Date: 20260127

Claims (9)

1. A tunable single longitudinal mode erbium-doped fiber laser based on double filters is characterized by comprising 976 nanometer pump sources, 976 nanometer/1550 nanometer wavelength division multiplexers, erbium-doped fibers, fiber isolators, a first filter, a second filter and a 90:10 fiber coupler; The output port of the 976 nanometer pump source is connected with the pump port of the 976 nanometer/1550 nanometer wavelength division multiplexer, the public end of the 976 nanometer/1550 nanometer wavelength division multiplexer is connected with the input end of the erbium-doped optical fiber, the output end of the erbium-doped optical fiber is connected with the input end of the optical fiber isolator, the output end of the optical fiber isolator is connected with the input end of the first filter, the output end of the first filter is connected with the input end of the second filter, the output end of the second filter is connected with the input end of the 90-to-10 optical fiber coupler, the feedback output end of the 90-to-10 optical fiber coupler is connected with the pump port of the 976 nanometer/1550 nanometer wavelength division multiplexer, and the output port of the 90-to-10 optical fiber coupler is used as the output port of the whole laser.
2. The tunable single longitudinal mode erbium-doped fiber laser based on double filters according to claim 1, wherein the first filter comprises a 3dB fiber coupler, a first uniform fiber grating and a second uniform fiber grating, the input end of the 3dB fiber coupler is connected with the output end of the fiber isolator, the two output ends of the 3dB fiber coupler are respectively connected with the first uniform fiber grating and the second uniform fiber grating, and the first uniform fiber grating and the second uniform fiber grating are respectively encapsulated on polytetrafluoroethylene materials with large temperature sensitivity coefficients.
3. The tunable single longitudinal mode erbium doped fiber laser based on double filters according to claim 2, wherein the second filter is composed of two cascaded 3 x 3 fiber couplers, the second filter includes a first 3 x 3 fiber coupler and a second 3 x 3 fiber coupler, the first port of the first 3 x 3 fiber coupler is connected to the input port of the 3dB fiber coupler, the second port of the first 3 x 3 fiber coupler is connected to the second port of the second 3 x 3 fiber coupler, the third port of the first 3 x 3 fiber coupler is connected to the third port of the second 3 x 3 fiber coupler, the fourth port of the first 3 x 3 fiber coupler is connected to the fourth port of the second 3 x 3 fiber coupler, and the first port of the second 3 x 3 fiber coupler is connected to the input port of the 90:10 fiber coupler.
4. The tunable single longitudinal mode erbium doped fiber laser based on double filters according to claim 3, wherein said 976 nm pump source, 976 nm/1550 nm wavelength division multiplexer, erbium doped fiber, fiber isolator, 3dB fiber coupler, uniform fiber grating one, uniform fiber grating two, 3 x 3 fiber coupler one, 3 x 3 fiber coupler two, 90 to 10 fiber coupler are all non-polarization maintaining devices.
5. The tunable single longitudinal mode erbium doped fiber laser based on double filters according to claim 2, wherein in the first filter, the bragg wavelength, the 3dB bandwidth of the reflection spectrum and the reflectivity of the first uniform fiber grating and the second uniform fiber grating are the same, but the distances from the first uniform fiber grating and the second uniform fiber grating to the 3dB fiber coupler are different, and the frequency interval of the laser after passing through the first filter can be expressed as: ; wherein c is the light velocity in vacuum, n is the effective refractive index of the single-mode fiber, L 1 is the distance from the first uniform fiber grating to the output end of the 3dB fiber coupler, and L 2 is the distance from the second uniform fiber grating to the output end of the 3dB fiber coupler.
6. The tunable single-longitudinal-mode erbium-doped fiber laser according to claim 3, wherein in the second filter, the output coupling ratio of the port one, the port two and the port three of the 3×3 fiber coupler is 1:1:1, and the output coupling ratio of the port one, the port two and the port three of the 3×3 fiber coupler is 1:1:1.
7. The tunable single longitudinal mode erbium doped fiber laser based on double filters according to claim 3, wherein there are two fiber loops in the second filter, the two fiber loops are two interference arm loops formed by connecting the port two of the 3 x 3 fiber coupler one with the port two of the 3 x 3 fiber coupler two, the port three of the 3 x 3 fiber coupler one with the port three of the 3 x 3 fiber coupler two, the port four of the 3 x 3 fiber coupler one with the port four of the 3 x 3 fiber coupler two, the free spectral ranges of the two fiber loops are FSR 1 and FSR 2 , respectively, according to vernier effect, due to the tiny difference of the lengths of the two fiber loops, extremely narrow transmission windows are generated only at the coincidence of the formants of the two fiber loops, the equivalent free spectral range FSR of the second filter is significantly amplified: ; therefore, only one ultra-narrow transmission peak is reserved in an extremely wide range, and the ultra-narrow band filtering effect is achieved on the longitudinal mode of the laser.
8. The tunable single longitudinal mode erbium-doped fiber laser based on double filters according to claim 2, wherein the wavelength tunable mode of the laser is temperature tuning, and the wavelength drift amounts of the uniform fiber grating one and the uniform fiber grating two after packaging are: ; Wherein, the The thermal expansion coefficient of the unpackaged fiber grating; The thermal-optical coefficient of the unpackaged fiber grating; the effective elastance coefficient of the uniform fiber bragg grating is; The thermal expansion coefficient of the polytetrafluoroethylene for encapsulation; When the external temperature rises, the polytetrafluoroethylene coating generates remarkable longitudinal extension, and the thermal expansion is converted into axial tensile strain on the fiber grating through interfacial adhesion, so that wide-range wavelength tuning is realized.
9. The dual-filter-based tunable single longitudinal mode erbium-doped fiber laser according to claim 1, wherein all devices in the tunable single longitudinal mode erbium-doped fiber laser are sequentially connected to each other by means of optical fiber fusion.

Description

Tunable single longitudinal mode erbium-doped fiber laser based on double filters Technical Field The invention belongs to the field of fiber lasers, and particularly relates to a tunable single longitudinal mode erbium-doped fiber laser based on a double filter. Background The single longitudinal mode erbium-doped fiber laser has the advantages of covering C+L communication wave bands, having narrow linewidth, high coherence, low noise, high beam quality and the like, and is widely applied to the fields of distributed sensing, coherent optical communication, optical measurement, laser radar and the like. Therefore, single longitudinal mode erbium doped fiber lasers have received much attention. In recent years, the optical fiber communication technology has rapidly developed, the requirements on communication light sources are higher and higher, and the optical fiber laser with fixed wavelength is greatly limited in communication transmission rate and transmission capacity. In addition, the tuning range of the single longitudinal mode fiber laser is usually narrow, and the tuning process is complex, so that the application requirement of a laser light source with wide wavelength tuning is difficult to be met by the common single longitudinal mode fiber laser. At present, the method for realizing the single longitudinal mode mainly comprises a linear short cavity method, an annular cavity method and a composite cavity method. The linear short cavity structure has low output power of the laser due to the short length of the gain fiber, the tuning range is limited, the annular cavity structure is easy to be interfered by external environment due to the long cavity length, the laser is difficult to realize single longitudinal mode stable operation, the free spectrum range is expanded by the composite cavity based on vernier effect, the single longitudinal mode laser output is realized, and the noise performance, the line width performance, the stability performance and the like of the output laser can be greatly improved by optimizing the composite cavity structure. The implementation method of the tunable technology mainly comprises a temperature tuning method, a stress tuning method, a tunable filter method and the like. The stress tuning method is limited by the tensile length of the fiber grating, and has the problems of hysteresis, slow adjustment, small tuning range and the like, the application of the tunable filter is limited due to higher device cost, and the temperature tuning mode also limits the tuning range due to smaller temperature sensitivity of the loaded unpackaged fiber grating. Disclosure of Invention Aiming at the problems existing in the prior art, the invention aims to provide a tunable single longitudinal mode erbium-doped fiber laser based on a double filter so as to realize the single longitudinal mode narrow linewidth and tunable wide wavelength output of laser, thereby solving the problems in the prior art. In order to achieve the above purpose, the present invention adopts the following technical scheme: A tunable single longitudinal mode erbium-doped fiber laser based on double filters comprises 976 nanometer pump source, 976 nanometer/1550 nanometer wavelength division multiplexer, erbium-doped fiber, fiber isolator, filter I, filter II, 90:10 fiber coupler; The output port of the 976 nanometer pump source is connected with the pump port of the 976 nanometer/1550 nanometer wavelength division multiplexer, the public end of the 976 nanometer/1550 nanometer wavelength division multiplexer is connected with the input end of the erbium-doped optical fiber, the output end of the erbium-doped optical fiber is connected with the input end of the optical fiber isolator, the output end of the optical fiber isolator is connected with the input end of the first filter, the output end of the first filter is connected with the input end of the second filter, the output end of the second filter is connected with the input end of the 90-to-10 optical fiber coupler, the feedback output end of the 90-to-10 optical fiber coupler is connected with the pump port of the 976 nanometer/1550 nanometer wavelength division multiplexer, and the output port of the 90-to-10 optical fiber coupler is used as the output port of the whole laser. Further, the first filter comprises a 3dB fiber coupler, a first uniform fiber grating and a second uniform fiber grating, wherein the input end of the 3dB fiber coupler is connected with the output end of the fiber isolator, the two output ends of the 3dB fiber coupler are respectively connected with the first uniform fiber grating and the second uniform fiber grating, and the first uniform fiber grating and the second uniform fiber grating are respectively packaged on polytetrafluoroethylene materials with large temperature sensitivity coefficients. Further, the second filter is composed of two cascaded 3×3 optical fiber couplers, the second filter comprises a first 3×