WO2009040465A2 - Amplificateur optique - Google Patents

Amplificateur optique Download PDF

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Publication number
WO2009040465A2
WO2009040465A2 PCT/FI2008/050513 FI2008050513W WO2009040465A2 WO 2009040465 A2 WO2009040465 A2 WO 2009040465A2 FI 2008050513 W FI2008050513 W FI 2008050513W WO 2009040465 A2 WO2009040465 A2 WO 2009040465A2
Authority
WO
WIPO (PCT)
Prior art keywords
fiber
optical amplifier
accordance
optical
bending plane
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/FI2008/050513
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English (en)
Other versions
WO2009040465A3 (fr
Inventor
Simo Tammela
Kalle YLÄ-JARKKO
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Corelase Oy
Original Assignee
Corelase Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Corelase Oy filed Critical Corelase Oy
Publication of WO2009040465A2 publication Critical patent/WO2009040465A2/fr
Publication of WO2009040465A3 publication Critical patent/WO2009040465A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06704—Housings; Packages
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/14—Mode converters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S2301/00—Functional characteristics
    • H01S2301/02—ASE (amplified spontaneous emission), noise; Reduction thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06754—Fibre amplifiers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08018—Mode suppression
    • H01S3/0804—Transverse or lateral modes
    • H01S3/08045—Single-mode emission
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094003—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre
    • H01S3/094007—Cladding pumping, i.e. pump light propagating in a clad surrounding the active core

Definitions

  • the present invention relates to an optical amplifier in accordance with the preamble of claim 1.
  • the present invention relates also to a method in connection with an optical amplifier.
  • the object of the present invention is to improve the discrimination between the fundamental and higher order core modes. This is achieved mainly by reducing the back coupling from the cladding modes to core modes, also called as resonance effect, in double cladding fibers.
  • the closest mode to the fundamental mode is asymmetric mode (LPl 1).
  • the optical power of the LPl 1 mode is in two side lobes, there is no power in the center.
  • Helical cladding modes are un-desirable modes in double cladding fiber.
  • optical powers of these cladding modes travel in a helical route in the cladding and these modes have very little, if any, optical power in the center part of the fiber where the doped core exist.
  • the pump light in these modes can not be absorbed by the core and thus the energy in these modes are carrying can not be used for amplification.
  • Several patents describe the ways to solve this problem; many of them describe how to break the circular symmetry of the cladding geometry. Unfortunately as the circular symmetry of the cladding is broken also the mechanical strength of the fiber is worse and especially the splicing of these non- circular fibers becomes difficult.
  • the fiber is coiled in such a manner that the plane where the fiber is curved / bent continuously changes thus removing the existence of 'horizontal' and 'vertical' higher order anti symmetric core LPl 1 modes, the undesired core modes are coupled into a large group of cladding modes thus removing the resonance effect and simultaneously causing coupling between the cladding modes that result strong diffusion to the helical modes.
  • the apparatus in accordance with invention is characterized by what is stated in the characterizing portion of Claim 1. More specifically, the method in accordance with invention is characterized by what is stated in the characterizing portion of Claim 13.
  • the discrimination between fundamental mode and higher order core modes can be improved by eliminating the resonance effects between the core modes and cladding modes. This improves the beam quality (less power at higher order modes), the efficiency can be improved (less gain for the un-wanted modes that are coupled to cladding), the tolerance for the active fiber core diameter and NA are larger.
  • the helical modes in the cladding are mixed with other modes and thus the absorption of the pump light carried with these modes is improved. This improves the efficiency by increasing the pump power which will be used for amplification
  • This method can be applied also for making a mode filter in a multimode fiber in which the un-wanted higher order modes are removed from the core by bending the multimode fiber as described in the characterizing portion of Claim 12.
  • FIG 1 shows schematically one optical amplifier in accordance with the invention.
  • FIG. 2 shows schematically another optical amplifier in accordance with the invention.
  • Figure 3 shows as a perspective view one embodiment how to spool an optical fiber around a cylindrical body in accordance with the invention.
  • Figure 4 shows as a perspective view one embodiment how to spool an optical fiber spirally on a curved body in accordance with the invention.
  • Figure 5 shows as a perspective view one embodiment how to spool an optical fiber spirally on a corrugated body in accordance with the invention.
  • Figure 6 shows a cross section of a typical optical fiber in accordance with the invention.
  • Figures 7a-7d show behaviour of the fundamental mode and the first higher order modes (LPl 1 modes) in the fiber when the fiber is bent and the bending plane has rocked 90 degrees from the beginning.
  • Figures 8a-8h show the behaviour of fundamental mode, the first higher order core modes (LPl 1 modes) and schematically the emerging cladding modes in the fiber when the fiber is bent and the bending plane is rocking so that the bending plane has turned 90 degree from the beginning.
  • Figure 9a shows as a top view another embodiment of the invention how to spool an optical fiber spirally on a corrugated body in accordance with the invention.
  • Figure 9b shows side view of the figure 9a.
  • Figure 10 shows as a perspective view one embodiment of the invention with a toroid body.
  • Figure 11 shows as a perspective view a tapering, helically spooled fiber in accordance with the invention.
  • Figure 12a shows as a top view another embodiment of the invention how to spool an optical fiber spirally on a corrugated body in accordance with the invention.
  • Figure 12b shows side view of the figure 12a.
  • Figure 13a shows as a top view another embodiment of the invention how to spool an optical fiber spirally on a curved body in accordance with the invention.
  • Figure 13b shows side view of the figure 13 a.
  • Figure 14a shows as a top view another embodiment of the invention how to spool an optical fiber spirally and in a sine wave format on a curved body in accordance with the invention.
  • Figure 14b shows side view of the figure 14a.
  • the optical amplifier 10 typically comprises a pump laser 1 and signal source 5, which are combined optically by a combiner 2.
  • Combiner 2 is further connected to an optical fiber 7, which is spooled on a cylindrical body 6, forming a fiber spool 3.
  • the signal is output 4 at the end of the fiber 7.
  • a sine form bending is performed on the cylinder surface of the body 6.
  • the fiber 7 bends all the time along the length of the cylinder 6 surface in three dimensions.
  • the sine wave form of the fiber takes care of bending in first two dimensions and the cylinder 6 surface takes care of the third dimension.
  • the cross- section of the cylinder 6 is not necessarily circular, although it can be. Also the radius of the cylinder can vary, see figure 11. In optimized situation the bending caused by the cylinder 6 should follow the sine form bending of the fibers in a manner that keeps the total fiber bending radius the same everywhere. In accordance with the invention instead of the sine wave form also waveforms close to sine or cosine can be used as well as combinations of continuous curvature and non-continuous curvatures.
  • Figure 2 shows the amplifier 10 in a laser configuration in which the laser cavity is formed by placing the amplifier 10 in between a mirror 5 operating as a high reflector in place of the signal source 5 of figure 1 and a mirror 4 operating as an output coupler.
  • Figure 3 shows the fiber spool 3 with its cylindrical body 6 in more detail. The fiber 7 is wound around the cylindrical surface of the body such that the continuous fiber 7 forms a sine wave figure on the cylinder surface. The form of the bending does not have to be pure sine waveform, the most important thing is the overall design of the changing bending direction of the fiber. Other examples will describe this in more detail.
  • the waist (circumference) of the cylinder 3 is an integer multiplier of the bending pitch ⁇ of the sine wave.
  • the diameter of the cylinder d is approximately 100 - 180 millimeters. These dimensions are suitable for a fiber with total diameter of 400 ⁇ m and core diameter of 20 ⁇ m.
  • Figure 4 shows another embodiment, where the fiber 7 is spooled spirally on a curved body 6.
  • the radius of curvature of the body 6 is approximately 50 - 100 mm and the diameter of the fiber bends on the surface are in the range of 100 - 200 mm when the core diameter of the fiber is 20 ⁇ m.
  • the fiber spool 3 is formed with an expanded spiral spooling of the fiber 7 on a corrugated body 6.
  • Figure 6 shows the principle structure of the fiber 7, comprising of a core 9 and a first cladding 8 surrounding it.
  • Second cladding 10 surrounds further the first cladding 8.
  • the refractive index decreases from the core 9 to the second cladding 10 such that the step of change in the refractive index is greater between first cladding 8 and second cladding 10 than between core 9 and the first cladding 8.
  • the pump light is coupled into the core 9 or alternatively the pump light is coupled into the first cladding layer 8.
  • the latter principle is used because the pump laser costs depend heavily on the pump fiber core diameter.
  • Typical bending radius for a 20 ⁇ m core fiber with NA of 0.06 - 0.08 varies froml5 mm up to 120 mm.
  • the pitch length (the distance where plane of the bending of the fiber are orthogonal) can be from 10 mm 400 mm depending on the mechanical design and the gain / length in the fiber.
  • Figures 7a-7d explain in connection with figure 3, how the higher order modes are leaked to the cladding when fiber is bent at position 0 the higher order anti symmetric mode at plane Y in figure 7b leaks to the cladding but not the same order of the mode at plane X.
  • the plane of the bending of the fiber has changed so that the mode at plane X in figure 7c is now leaking and not the mode at plane Y in figure 7d.
  • Figures 8a-8h show that as the curvature plane rocks the higher order core modes couple into a set of cladding modes instead of a few of them.
  • FIG. 8a and 8b correspond to figures 7a and 7b at position 0 of figure 3.
  • Figures 8g and 8h respectively correspond to figures 7b and 7b at position ⁇ /2 of the spool 3 of figure 3.
  • Figures 8 c- 8 f represent the intermediate positions between positions 0 and ⁇ /2 of the spool 3 of figure 3.
  • the rocking of the curvature plane removes the resonance behavior of the core mode leaking into cladding modes. This also enhances the mode coupling of the cladding modes and thus further increases the diffusion of the light between the cladding modes.
  • the increased coupling of the higher order modes into cladding modes by bending the fiber can be explained by looking into the propagation constants of the different modes within the fiber core.
  • the propagation constant of the higher order modes are closer to the propagation constants of the cladding modes and thus the criterion for the slow variation of the waveguide for the adiabatic waveguide modulation is tighter than that of the fundamental mode.
  • this difference is further increased as the propagation modes of the cladding modes increase and come closer to the propagation modes of the core modes.
  • the modulation of the refractive index profile that is due to the change of bending
  • the coupling between the higher order / asymmetric / core modes and the cladding modes is enhanced.
  • the rocking motion is preferentially continuous in both the planes along the fiber length with a constant pitch and amplitude.
  • pitch and amplitude can be varied and/or the rocking motion can be divided in three or more phases, see figures 12 and 13.
  • the amplitude is determined by the applicable radius of the curvature corresponding to the desired output beam quality as defined by the fiber core diameter and core numerical aperture, for example on the same manner as in US6496301.
  • Basic rule of thumb is that to achieve operation close to the fundamental mode the chosen radius of curvature is smaller in order to have higher discrimination between the fundamental and higher order modes. In case the operation of the amplifier is desired to be multimode the radius of curvature is increased.
  • figures 9a and 9b is presented a combination of sinusoidal modulation of the fiber 7 on the surface 6 and in the fiber spiral spool.
  • the pitch on the modulation is the same both on the surface 6 and on the fiber 7, but there is a ⁇ /4 phase shift between the modulations.
  • figure 10 is presented a helical fiber 7 formed on a toroid body 6.
  • the rocking of the refractive index profile is optimum when the pitch is equal to pi*diameter of the toroid body 6.
  • figure 11 is presented a tapering helically spooled fiber 7.
  • the bending radius of the cylinder 6 is constantly decreasing throughout the cylinder length, i.e. di>d 2 .
  • Figures 12a and 12b represent a slight modification of the embodiment of figures 9a and 9b such that the sine wave form is not used in spooling. Spooling is made only spirally.
  • Figures 13a and 13b represent a slight modification of the embodiment of figures 12a and 12b such that the body 6 is not corrugated but comprises a single curved projecting part instead of the corrugations.
  • Figures 14a and 14b represent a combination of the body 6 of figures 13a and 13 b and the spooling of fiber 7 in an essentially similar way as in figures 9a and 9b.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Plasma & Fusion (AREA)
  • General Physics & Mathematics (AREA)
  • Lasers (AREA)

Abstract

La présente invention concerne un amplificateur optique (10) qui utilise une fibre optique multimode (7), comprenant un laser à pompe (1), une fibre optique (7), qui forme un guide d'ondes et possède au moins partiellement un rayon de courbure destiné à causer des pertes pour les modes d'ordre supérieur, connectée à l'amplificateur optique (1). Selon l'invention, la fibre (7) possède au moins sur une partie de sa longueur un changement continu du plan de courbure en trois dimensions de sorte que l'indice de réfraction effectif résultant du guide d'ondes bascule dans deux directions ou plus.
PCT/FI2008/050513 2007-09-28 2008-09-17 Amplificateur optique Ceased WO2009040465A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20075685 2007-09-28
FI20075685A FI20075685A0 (fi) 2007-09-28 2007-09-28 Optinen vahvistin

Publications (2)

Publication Number Publication Date
WO2009040465A2 true WO2009040465A2 (fr) 2009-04-02
WO2009040465A3 WO2009040465A3 (fr) 2009-08-20

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PCT/FI2008/050513 Ceased WO2009040465A2 (fr) 2007-09-28 2008-09-17 Amplificateur optique

Country Status (2)

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FI (1) FI20075685A0 (fr)
WO (1) WO2009040465A2 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100303409A1 (en) * 2009-05-29 2010-12-02 Pei-Cheng Ku Solid state light source based on hybrid waveguide-down-converter-diffuser
CN102147551A (zh) * 2011-04-01 2011-08-10 国神光电科技（上海）有限公司 多模光纤放大器及多模光纤放大系统
CN112751253A (zh) * 2020-12-29 2021-05-04 苏州创鑫激光科技有限公司 信号光高阶模滤除方法、高阶模滤除放大光路及激光器
WO2024213586A1 (fr) * 2023-04-14 2024-10-17 Trumpf Laser Uk Limited Fibre optique et dispositif à fibre optique

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2548278A1 (de) * 1975-10-28 1977-05-05 Siemens Ag Magnetooptischer strom-messwandler
AU624445B2 (en) * 1988-11-15 1992-06-11 Hughes Aircraft Company Method and apparatus for winding flat coils of filamentary materials such as optical fibers
CH683950A5 (fr) * 1991-04-04 1994-06-15 Suisse Electronique Microtech Procédé de réalisation d'une bobine à fibre optique monomode, bobine ainsi obtenue et utilisation de cette bobine.
WO2005022705A2 (fr) * 1997-03-21 2005-03-10 Imra America, Inc. Amplificateur a fibre optique haute energie pour impulsions picoseconde-nanoseconde destinees a des applications de traitement de materiaux hautes performances
US6496301B1 (en) * 2000-03-10 2002-12-17 The United States Of America As Represented By The Secretary Of The Navy Helical fiber amplifier
US6912342B2 (en) * 2002-12-19 2005-06-28 Corning Incorporated Optical fiber module having reduced multi-path interference

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100303409A1 (en) * 2009-05-29 2010-12-02 Pei-Cheng Ku Solid state light source based on hybrid waveguide-down-converter-diffuser
CN102449387A (zh) * 2009-05-29 2012-05-09 密执安州立大学董事会 基于混合波导-下转换器-扩散器的固态光源
US8768108B2 (en) * 2009-05-29 2014-07-01 The Regents Of The University Of Michigan Solid state light source based on hybrid waveguide-down-converter-diffuser
CN102147551A (zh) * 2011-04-01 2011-08-10 国神光电科技（上海）有限公司 多模光纤放大器及多模光纤放大系统
WO2012130135A1 (fr) * 2011-04-01 2012-10-04 国神光电科技（上海）有限公司 Amplificateur à fibre optique multimodale et système d'amplification à fibre optique multimodale
CN112751253A (zh) * 2020-12-29 2021-05-04 苏州创鑫激光科技有限公司 信号光高阶模滤除方法、高阶模滤除放大光路及激光器
WO2024213586A1 (fr) * 2023-04-14 2024-10-17 Trumpf Laser Uk Limited Fibre optique et dispositif à fibre optique

Also Published As

Publication number Publication date
WO2009040465A3 (fr) 2009-08-20
FI20075685A0 (fi) 2007-09-28

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