CN103840359B - A kind of tunable multi-wavelength is stablized narrow cable and wide optical fiber laser - Google Patents

Abstract

This patent relates to a ring-structured multi-wavelength fiber laser, especially a tunable multi-wavelength fiber laser, which belongs to the field of laser technology. The light emitted by the pump source passes through the wavelength division multiplexer (WDM) and enters the erbium-doped fiber to obtain optical gain, and then enters the two parallel sagnac rings through the first coupler in two ways, and comes out from the two sagnac rings The light from the isolator enters the fourth coupler, the light from the isolator enters the tunable fiber grating, the light from the tunable fiber grating enters the fifth coupler, and the fifth coupler is a 90:10 coupler that converts the incoming light Divided into two circuits, 10% of which is used as output light, 90% is fed back to the wavelength division multiplexer along the optical fiber, and the above process is repeated. When the gain of the entire loop is greater than the loss, a stable tunable multi The wavelength of laser output, the direction of light entering and exiting the first coupler and the fourth coupler is just opposite.

Description

A tunable multi-wavelength stable narrow-linewidth fiber laser

Technical field:

This patent relates to a ring-structured multi-wavelength fiber laser, especially a tunable multi-wavelength fiber laser, which belongs to the field of laser technology.

Background technique:

With the development of high-capacity optical fiber communication networks, wavelength division multiplexing technology has become the mainstream technology for long-distance communication trunk lines and optical networks. As an important light source in wavelength routing networks, multi-wavelength fiber lasers can effectively avoid channel conflicts and become a research hotspot. At the same time, multi-wavelength fiber lasers have the advantages of narrow line width, high output power, good stability, and easy compatibility with fiber optic communication systems, making them have broad application prospects in fiber optic sensing systems, optical testing, and spectroscopy.

The traditional multi-wavelength signal source consists of a series of single-wavelength DFB semiconductor lasers. The technology is relatively simple. The disadvantage is that the system is huge and the cost is high. The problem is more prominent when considering the optical network with optical cross nodes. And from the perspective of simplifying the structure, reducing costs, and facilitating maintenance, multi-wavelength fiber lasers that can realize channel spacing and channel number adjustment have obvious application advantages.

For this application goal, a lot of research work has been done. In the article entitled "16-Wavelength10-GHzActivelyMode-LockedFiberLaserWithDemultiplexedOutputsAnchoredontheITU-TGrid" published in Photon Technology Letters (IEEEPTL) by RieHayashi et al. in December 2003, an erbium-doped fiber cooled to liquid nitrogen temperature (77K) was used as the gain medium , a feedback loop composed of a circulator and a lithium niobate external modulator is used as one end of the resonant cavity, and a waveguide array with a reflectivity of 90% is used as the other end of the resonant cavity and also as a wavelength selector, realizing 16 wavelengths, Mode-locked pulse output with a wavelength interval of 100GHz. However, due to the uniform broadening of the gain of erbium-doped fiber at room temperature, it is only possible to achieve multi-wavelength stable output at a very low temperature, which is a big problem in practical applications.

Realizing adjustable output wavelength at room temperature, adjustable output wavelength interval and adjustable output channel number have always been the focus of research on multi-wavelength lasers. In recent years, there have been many methods such as: introducing frequency shift feedback mechanism, dual-core erbium-doped fiber, elliptical erbium-doped fiber, acousto-optic frequency shifter, sinusoidal phase modulator, four-wave mixing effect, etc., but the structure of these methods is relatively complicated And some require special treatment for the gain fiber, and some require special equipment, which is not conducive to low cost and integration.

In 2005, Young-GeunHan and GilhwanKim published an article titled "LasingWavelengthandSpacingSwitchableMultiwavelengthFiberLaserFrom1510to1620nm" on PhotonicsTechnologyLetters, IEEE, which reported that they obtained a normal temperature laser with adjustable output wavelength between 1510nm and 1620nm, adjustable wavelength interval and adjustable output channel number. A stable multi-wavelength fiber laser. The main body of its experimental device is composed of mixed gain media (SOA, C-band EDFA, L-band EDFA) and tunable PMFLyot-Sagnac filter. The self-saturation effect of the semiconductor optical amplifier is used to obtain stable multi-wavelength laser output with high signal-to-noise ratio, and the nonlinear gain suppression of SOA can also be used to adjust the output wavelength. However, SOA is not an all-optical device, the coupling loss is relatively large, and the output power is greatly limited.

The multi-wavelength erbium-doped fiber laser based on Brillouin scattering is also a research hotspot in recent years. This type of laser combines the linear gain of erbium-doped fiber and the nonlinear gain of Brillouin scattering, and is an effective method to generate multi-wavelength output at room temperature. , however, due to the small nonlinear gain coefficient of stimulated Brillouin scattering, it generally requires a longer fiber length and a larger pump power, which also has a great limitation on the improvement of the output characteristics.

Another common structure to achieve multi-wavelength output is the use of Mach-Zehnder interferometers. In 2007, Chen, Daru et al. published an article titled "Channel-spacing-tunablemulti-wavelength fiberringlaser with hybridRamanandErbium-dopedfibergains" on OPTICSEXPRES for Mach- The Zehnder interferometer is improved, and the variable optical delay line Mach-Zehnde interferometer is used to realize the multi-wavelength fiber laser with variable channel spacing at room temperature, but the variable optical delay line needs to be controlled by a computer, which is not conducive to the overall packaging of the system. And such lasers are usually not tunable.

In 2008, ThiVanAnhTran et al. published on OPTICS EXPRESS entitled "SwitchablemultiwavelengththerbiumdopedfiberlaserbasedonanonlinearopticalloopmirrorincorporatingmultiplefiberBragggratings", a multi-channel filter composed of a highly nonlinear dispersion-shifted fiber combined with a waveguide array grating connected to multiple fiber gratings was realized at room temperature. Multi-wavelength tunable output. In its structure, multiple fiber gratings are connected to the waveguide array grating, the structure is complex, and the introduction of multiple fusion points causes a large loss.

In conclusion, so far, the technology of simultaneously realizing multi-wavelength output lasers has not been able to meet the needs of applications.

Invention content:

The technical problem to be solved by the invention is to solve the problems in the prior art such as poor tunability, low stability, complicated narrow line width output process and the like.

The technical solution adopted in the present invention is: a tunable multi-wavelength stable narrow-linewidth fiber laser, the light emitted by the pump source passes through a wavelength division multiplexer (WDM) and then enters the erbium-doped optical fiber to obtain optical gain, and then passes through the first A coupler divides into two paths and enters the two parallel sagnac rings respectively, the light from the two sagnac rings enters the fourth coupler, the light from the isolator enters the tunable fiber grating, and the light from the tunable fiber grating Enter the fifth coupler, the fifth coupler is a 90:10 coupler that divides the incoming light into two paths, 10% of which is used as output light, and 90% is fed back to the wavelength division multiplexer along the optical fiber, and the above process is repeated. When the gain of the entire loop is greater than the loss, a stable tunable multi-wavelength laser output is obtained at the output of the fifth coupler, the first coupler is a 50:50 coupler, and the fourth coupler is a 50:50 coupling The light entering and exiting directions of the first coupler and the fourth coupler are just opposite.

As a preferred manner: the two sagnac rings are a first sagnac ring and a second sagnac ring, the first sagnac ring includes a second coupler, a first polarization controller, a second polarization controller, a first chirped fiber grating, The first polarization maintaining fiber, the second polarization maintaining fiber, the second sagnac ring includes a third coupler, a third polarization controller, a fourth polarization controller, a second chirped fiber grating, a third polarization maintaining fiber, a fourth polarization Keeping the fiber, the second coupler is a 50:50 coupler and the third coupler is a 50:50 coupler.

The beneficial effects of the present invention are: by changing the polarization state of the light in the two sagnac rings, the two columns of light waves that meet in the chirped fiber grating are two beams of light with the same polarization state in opposite directions, and the polarization-maintaining fiber is obtained through analysis. The optimal length makes the two beams of light have a certain phase difference, and interference occurs during their retransmission, so that the linewidth of the multi-wavelength outgoing light obtained in the chirped grating is narrower. At the same time, the introduction of polarization-dependent components into the device can effectively suppress the uniform broadening bandwidth of the erbium-doped fiber, and achieve stable multi-wavelength fiber laser output at room temperature. This patent adopts the structure of two sagnac rings connected in parallel, which has a good narrowing effect on the line width of the obtained multi-wavelength outgoing light. A broadband tunable fiber grating is used as the wavelength adjustment element. A 90:10 output coupler feeds most of the optical power back into the fiber ring cavity, and the optical coupler and optical isolator whose working wavelength covers the output wavelength range are selected. The invention does not need to place the gain medium in liquid nitrogen, nor does it need complex and expensive devices, and has a simple structure, easy realization and low cost, and has good application prospects.

Description of drawings:

Fig. 1 is a schematic diagram of the invention structure;

Fig. 2 is a schematic diagram of the structure of the first sagnac ring of the present invention;

Among them: 1. Pump source, 2. Wavelength division multiplexer, 3. Erbium-doped fiber, 4. First coupler, 5a, Second coupler, 5b, First polarization controller, 5c, Second polarization control device, 5d, the first chirped fiber grating, 5e, the first polarization maintaining fiber, 5f, the second polarization maintaining fiber, 6a, the third coupler, 6b, the third polarization controller, 6c, the fourth polarization controller, 6d, second chirped fiber grating, 6e, third polarization maintaining fiber, 6f, fourth polarization maintaining fiber, 7: fourth coupler; 8: isolator; 9: tunable fiber Bragg grating; 10: fifth coupler .

detailed description:

As shown in Figure 1, a semiconductor laser with an output wavelength of 980nm is used as the pumping source. The pumping light generated by the pumping source 1 is coupled into the loop through the 980nm port of the wavelength division multiplexer 2. In 3 (EDF), the population inversion occurs and the optical gain is obtained at the same time. The gain light is divided into two paths by a 50:50 first coupler 4, and enters the coupler composed of the second coupler 5a and the third coupler 6a respectively. In the two sagnac rings, and the first sagnac ring here is embedded with a section of the first chirped fiber grating 5d, and the second sagnac ring is embedded with a section of the second chirped fiber grating 6d, utilizing the first chirped fiber grating 5d and the second According to the filtering characteristics of the chirped fiber grating 6d, a beam of multi-wavelength light is respectively obtained in the two paths. The first chirped fiber Bragg grating 5d and the second chirped fiber Bragg grating 6d can be achieved by reasonably selecting the periodic phase shift and chirp coefficient of the chirped fiber of the first chirped fiber Bragg grating 5d and the second chirped fiber Bragg grating 6d Precise control of channel spacing and number of channels.

The transmission characteristics of the two sagnac rings are related to the birefringence characteristics of their internal optical paths. The structures of the two sagnac rings of the present invention are similar, and are currently described with the first sagnac ring, with the first sagnac ring of the first chirped fiber grating 5d The structure is shown in Figure 2. It consists of a 3dB coupler 5a (the second coupler) and the first chirped fiber grating 5d. The input and output ports are I and II. The first polarization controller 5b is added to the first sagnac ring , a second polarization controller 5c, a first polarization maintaining fiber 5e, and a second polarization maintaining fiber 5f. The lengths of the first polarization-maintaining fiber 5e and the second polarization-maintaining fiber 5f are L1 and L2 respectively, and the incident light from the port I is divided into two paths by the 3dB coupler 5a, and is incident on the first chirped fiber grating 5d from two directions, The polarization states of the two beams of light can be kept consistent by controlling the first polarization controller 5b and the second polarization controller 5c, so that under the filtering effect of the first chirped fiber Bragg grating 5d, the propagation directions are opposite and the polarization states are the same The two beams of multi-wavelength beams, the condition here is that the two arms L1 and L2 of the first sagnac ring are equal. The optimum lengths of the first polarization maintaining fiber 5e and the second polarization maintaining fiber 5f can be found by design, so that the two beams of counter-propagating light have a certain phase difference, and interference occurs during its propagation, so that the obtained multi-wavelength The line width of the outgoing light is narrowed, and the multi-wavelength output light exits through the port II of the second coupler 5a.

Polarization dependent elements (first polarization controller, second polarization controller, third polarization controller, fourth polarization controller, first polarization maintaining fiber, second polarization maintaining fiber, third polarization maintaining fiber, The fourth polarization-maintaining fiber) can effectively suppress the uniform broadening bandwidth of the erbium-doped fiber, and realize stable multi-wavelength fiber laser output at room temperature.

The present invention uses two sagnac rings with chirped fiber gratings to be connected in parallel, and interference occurs when the two beams of light pass through the fourth coupler 7, so that the obtained multi-wavelength output line width is narrower. At the same time, the invention does not require that the chirped fiber gratings in the two sagnacs are completely consistent, which reduces the difficulty of making the fiber gratings. More importantly, the use of this parallel structure greatly improves the stability of the output wavelength, and can further narrow the linewidth.

The multi-wavelength light emitted by the fourth coupler 7 passes through a broadband tunable fiber grating 9 for wavelength selective output, thereby realizing a stable laser output with adjustable wavelength of output light and adjustable channel spacing. Here, the tunable fiber grating 9 requires a wide bandwidth in order to select a suitable laser output from multi-wavelength beams, and only light waves satisfying the Bragg conditions of the fiber grating can be output.

The function of the optical isolator 8 is to prevent the light emitted from the fourth coupler 7 from returning to the fourth coupler 7 to affect the optical ring circuit, so as to ensure that the light propagates clockwise in the entire ring cavity.

The light passing through the tunable fiber grating 9 is divided into two paths through a 90:10 fifth coupler 10, 10% of which is used as output light, and 90% is fed back to the wavelength division multiplexer 2 along the optical fiber, and the above process is repeated. When the gain of the entire loop is greater than the loss, a stable and tunable multi-wavelength laser output is obtained at the output end of the fifth coupler 10 .

Claims (2)

1. a tunable multi-wavelength is stablized narrow cable and wide optical fiber laser, it is characterized in that: the light that pumping source sends enters after by wavelength division multiplexer and in erbium-doped fiber, obtains the gain of light, then divide two-way to enter respectively in two sagnac rings arranged side by side by the first coupler, the light that encircles out from two sagnac enters the 4th coupler, enter isolator from the 4th coupler light out, enter adjustable optic fibre grating from isolator light out, enter the 5th coupler from adjustable optic fibre grating light out, the 5th coupler is that the coupler of a 90:10 is divided into two-way the light entering, wherein 10% as output light, 90% feeds back to wavelength division multiplexer along optical fiber, repeat said process, when whole loop gain is greater than loss, obtain stable tunable multi-wavelength Laser output at the output of the 5th coupler, the first coupler is the coupler of a 50:50, the 4th coupler is the coupler of a 50:50, the light turnover direction of the first coupler and the 4th coupler is just contrary.

2. a kind of tunable multi-wavelength according to claim 1 is stablized narrow cable and wide optical fiber laser, it is characterized in that: two sagnac rings are a sagnac ring and the 2nd sagnac ring, the one sagnac ring comprises the second coupler, the first Polarization Controller, the second Polarization Controller, the first chirped fiber grating, the first polarization-maintaining fiber, the second polarization-maintaining fiber, the 2nd sagnac ring comprises the 3rd coupler, the 3rd Polarization Controller, the 4th Polarization Controller, the second chirped fiber grating, the 3rd polarization-maintaining fiber, the 4th polarization-maintaining fiber, the second coupler is the coupler of a 50:50, the 3rd coupler is the coupler of a 50:50.