Stabilised C-band dual wavelength erbium doped fibre ring laser
- Authors: Mthukwane, Clarence Modise
- Date: 2018
- Subjects: Optical fibers , Lasers - Industrial applications , Optical amplifiers , Bragg gratings , Erbium
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/280397 , uj:30130
- Description: M.Ing. (Electrical Engineering) , Abstract: In this dissertation, the realisation of a dual wavelength erbium doped fibre ring cavity laser configuration is discussed. The power stability and wavelength stability of a dual wavelength erbium doped fibre laser is investigated. The lasing wavelengths of the fibre laser are 1555.12 nm and 1560.32 nm. The laser is based on a ring cavity resonator which employs a 3 dB coupler and fibre Bragg gratings, as the wavelength selective component arrangement. The active medium in the cavity is a 3.2 m long erbium doped fibre with an absorption of 11.38 dB/m at 980 nm. To achieve simultaneous dual wavelength lasing with an erbium doped fibre laser configuration, there is one major challenge that must be overcome. The challenge is to correct the cavity losses on the selected wavelengths to achieve oscillation for all desired channels. In addition, because of the unevenness of the EDF gain profile, the threshold power for individual wavelengths is different. Subsequently, loss control across each of the selected wavelengths is required to balance the power difference between the wavelengths. The power and wavelength stability of the dual lasing wavelengths is investigated using an optical loop mirror with a 1 m length of single-mode fibre, and an unpumped erbium doped fibre of length 0.5 m, 1 m and 1.5 m. Also, the effect of changing the cavity length on the uniformity of the wavelength power increase relative to an increase in pump power together with the power and spectral stability of the lasing wavelengths is investigated. A 1m long Sagnac loop with a 70:30 coupling ratio was used to adjust the threshold power for simultaneous lasing of the two wavelengths. An increase in cavity length led to a good prospect for a stable dual wavelength laser with an output power difference of 0.4 dBm between the dual wavelengths and a power stability of 0.4 dB. The multi-wavelength and narrow spectral width of 0.19 nm and 0.20 nm of the laser can be used for dispersion measurement in wavelength division multiplexed communication links which consist of more than one wavelength. The laser was characterised for simultaneous dual wavelength output power response and power stability. The project presents the characterisation of an erbium doped fibre ring laser. The laser is cost effective and flexible in selecting preferred components for optimal performance in terms of power and wavelength stability, wavelength selectivity and narrow spectral width. Erbium doped fibre ring laser lasers are commercially available and are showing great promise in terms of their formidability and compatibility with current industrial requirements.
- Full Text:
- Authors: Mthukwane, Clarence Modise
- Date: 2018
- Subjects: Optical fibers , Lasers - Industrial applications , Optical amplifiers , Bragg gratings , Erbium
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/280397 , uj:30130
- Description: M.Ing. (Electrical Engineering) , Abstract: In this dissertation, the realisation of a dual wavelength erbium doped fibre ring cavity laser configuration is discussed. The power stability and wavelength stability of a dual wavelength erbium doped fibre laser is investigated. The lasing wavelengths of the fibre laser are 1555.12 nm and 1560.32 nm. The laser is based on a ring cavity resonator which employs a 3 dB coupler and fibre Bragg gratings, as the wavelength selective component arrangement. The active medium in the cavity is a 3.2 m long erbium doped fibre with an absorption of 11.38 dB/m at 980 nm. To achieve simultaneous dual wavelength lasing with an erbium doped fibre laser configuration, there is one major challenge that must be overcome. The challenge is to correct the cavity losses on the selected wavelengths to achieve oscillation for all desired channels. In addition, because of the unevenness of the EDF gain profile, the threshold power for individual wavelengths is different. Subsequently, loss control across each of the selected wavelengths is required to balance the power difference between the wavelengths. The power and wavelength stability of the dual lasing wavelengths is investigated using an optical loop mirror with a 1 m length of single-mode fibre, and an unpumped erbium doped fibre of length 0.5 m, 1 m and 1.5 m. Also, the effect of changing the cavity length on the uniformity of the wavelength power increase relative to an increase in pump power together with the power and spectral stability of the lasing wavelengths is investigated. A 1m long Sagnac loop with a 70:30 coupling ratio was used to adjust the threshold power for simultaneous lasing of the two wavelengths. An increase in cavity length led to a good prospect for a stable dual wavelength laser with an output power difference of 0.4 dBm between the dual wavelengths and a power stability of 0.4 dB. The multi-wavelength and narrow spectral width of 0.19 nm and 0.20 nm of the laser can be used for dispersion measurement in wavelength division multiplexed communication links which consist of more than one wavelength. The laser was characterised for simultaneous dual wavelength output power response and power stability. The project presents the characterisation of an erbium doped fibre ring laser. The laser is cost effective and flexible in selecting preferred components for optimal performance in terms of power and wavelength stability, wavelength selectivity and narrow spectral width. Erbium doped fibre ring laser lasers are commercially available and are showing great promise in terms of their formidability and compatibility with current industrial requirements.
- Full Text:
Instembare erbiumgedoteerde optiesevesellasers met nou lynwydtes
- Badenhorst, Christiaan Gerhardus
- Authors: Badenhorst, Christiaan Gerhardus
- Date: 2015-02-16
- Subjects: Lasers , Data communication , Erbium , Optical fibers
- Type: Thesis
- Identifier: uj:13340 , http://hdl.handle.net/10210/13354
- Description: M.Ing. , Please refer to full text to view abstract
- Full Text:
- Authors: Badenhorst, Christiaan Gerhardus
- Date: 2015-02-16
- Subjects: Lasers , Data communication , Erbium , Optical fibers
- Type: Thesis
- Identifier: uj:13340 , http://hdl.handle.net/10210/13354
- Description: M.Ing. , Please refer to full text to view abstract
- Full Text:
Numerical modelling of an Erbium-Ytterbium co-doped distributed feedback fiber laser
- Authors: Mpoyo, Justice Sompo
- Date: 2015-06-26
- Subjects: Erbium , Fiber optics , Optical communications , Bragg gratings
- Type: Thesis
- Identifier: uj:13635 , http://hdl.handle.net/10210/13815
- Description: M.Phil. (Electrical and Electronic Engineering) , A numerical model of an Erbium-Ytterbium co-doped distributed feedback (DFB) fiber laser is developed. The DFB fiber laser is a short length fiber laser whose feedback is distributed throughout the cavity. Its main advantage is its single longitudinal mode operation. The amplifying medium of a DFB fiber laser is a few centimetres long rare earth doped fiber. The feedback is obtained by a fibre Bragg grating printed in the core of the rare earth doped fiber. This type of laser emits naturally in two longitudinal modes. To obtain the single longitudinal mode operation, a π phase shift is introduced in the middle of the grating. Erbium doped DFB fiber lasers present the advantage of emitting single frequency light in the 1550 nm region where telecommunication fibers present the minimum loss. However due to the relatively short length of the gain medium, the number of available Erbium ions is small; as a result pump power absorption is low and the efficiency of the fiber laser is strongly reduced. The straightforward solution to this problem could be increasing the concentration of Erbium ions. This solution however has the disadvantage of increasing the Erbium ions interactions, thus leading to detrimental effect like cooperative upconversion and excited state absorption, which in term reduce considerably the laser efficiency. The best solution is to use Ytterbium ions as sensitizers along with Erbium ions to enhance the pump absorption, hence the efficiency of the laser. A model of the DFB fiber laser is an indispensable tool for its design, because it allows one to predict characteristic behaviour that would be both difficult and costly to deduce in laboratory conditions. The model developed in this project is based on rate equations of the Er3+-Yb3+ gain medium and coupled mode equations describing the laser field propagation in the fibre Bragg grating structure. The equations are solved using a quasi-analytical iterative method along with transfer matrix method with appropriate boundary conditions. The quasianalytical method used in this thesis is more robust than numerical solutions because it does not require providing an initial guess on the solution. Furthermore this method is hundreds time faster than the exact numerical solution while giving almost similar results.
- Full Text:
- Authors: Mpoyo, Justice Sompo
- Date: 2015-06-26
- Subjects: Erbium , Fiber optics , Optical communications , Bragg gratings
- Type: Thesis
- Identifier: uj:13635 , http://hdl.handle.net/10210/13815
- Description: M.Phil. (Electrical and Electronic Engineering) , A numerical model of an Erbium-Ytterbium co-doped distributed feedback (DFB) fiber laser is developed. The DFB fiber laser is a short length fiber laser whose feedback is distributed throughout the cavity. Its main advantage is its single longitudinal mode operation. The amplifying medium of a DFB fiber laser is a few centimetres long rare earth doped fiber. The feedback is obtained by a fibre Bragg grating printed in the core of the rare earth doped fiber. This type of laser emits naturally in two longitudinal modes. To obtain the single longitudinal mode operation, a π phase shift is introduced in the middle of the grating. Erbium doped DFB fiber lasers present the advantage of emitting single frequency light in the 1550 nm region where telecommunication fibers present the minimum loss. However due to the relatively short length of the gain medium, the number of available Erbium ions is small; as a result pump power absorption is low and the efficiency of the fiber laser is strongly reduced. The straightforward solution to this problem could be increasing the concentration of Erbium ions. This solution however has the disadvantage of increasing the Erbium ions interactions, thus leading to detrimental effect like cooperative upconversion and excited state absorption, which in term reduce considerably the laser efficiency. The best solution is to use Ytterbium ions as sensitizers along with Erbium ions to enhance the pump absorption, hence the efficiency of the laser. A model of the DFB fiber laser is an indispensable tool for its design, because it allows one to predict characteristic behaviour that would be both difficult and costly to deduce in laboratory conditions. The model developed in this project is based on rate equations of the Er3+-Yb3+ gain medium and coupled mode equations describing the laser field propagation in the fibre Bragg grating structure. The equations are solved using a quasi-analytical iterative method along with transfer matrix method with appropriate boundary conditions. The quasianalytical method used in this thesis is more robust than numerical solutions because it does not require providing an initial guess on the solution. Furthermore this method is hundreds time faster than the exact numerical solution while giving almost similar results.
- Full Text:
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