WO2002093697A2 - Fiber laser having a suppressor - Google Patents

Fiber laser having a suppressor

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Publication number
WO2002093697A2
WO2002093697A2 PCT/US2002/014926 US0214926W WO2002093697A2 WO 2002093697 A2 WO2002093697 A2 WO 2002093697A2 US 0214926 W US0214926 W US 0214926W WO 2002093697 A2 WO2002093697 A2 WO 2002093697A2
Authority
WO
Grant status
Application
Patent type
Prior art keywords
reflectors
energy
optical fiber
fiber
configured
Prior art date
Application number
PCT/US2002/014926
Other languages
French (fr)
Other versions
WO2002093697A3 (en )
Inventor
Andrey A. Demidov
Original Assignee
Optical Power Systems Incorporated
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

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Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES USING STIMULATED EMISSION
    • H01S3/00Lasers, i.e. devices for generation, amplification, modulation, demodulation, or frequency-changing, using stimulated emission, of infra-red, visible, or ultra-violet waves
    • H01S3/30Lasers, i.e. devices for generation, amplification, modulation, demodulation, or frequency-changing, using stimulated emission, of infra-red, visible, or ultra-violet waves using scattering effects, e.g. stimulated Brillouin or Raman effects
    • H01S3/302Lasers, i.e. devices for generation, amplification, modulation, demodulation, or frequency-changing, using stimulated emission, of infra-red, visible, or ultra-violet waves using scattering effects, e.g. stimulated Brillouin or Raman effects in an optical fibre
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES USING STIMULATED EMISSION
    • H01S3/00Lasers, i.e. devices for generation, amplification, modulation, demodulation, or frequency-changing, using stimulated emission, of infra-red, visible, or ultra-violet waves
    • H01S3/05Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06Construction or shape of active medium
    • H01S3/063Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067Fibre lasers
    • H01S3/0675Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES USING STIMULATED EMISSION
    • H01S3/00Lasers, i.e. devices for generation, amplification, modulation, demodulation, or frequency-changing, using stimulated emission, of infra-red, visible, or ultra-violet waves
    • H01S3/05Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06Construction or shape of active medium
    • H01S3/063Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067Fibre lasers
    • H01S3/06791Fibre ring lasers
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES USING STIMULATED EMISSION
    • H01S3/00Lasers, i.e. devices for generation, amplification, modulation, demodulation, or frequency-changing, using stimulated emission, of infra-red, visible, or ultra-violet waves
    • H01S3/05Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08Construction or shape of optical resonators or components thereof
    • H01S3/08004Construction or shape of optical resonators or components thereof incorporating a dispersive element, e.g. a prism for wavelength selection
    • H01S3/08009Construction or shape of optical resonators or components thereof incorporating a dispersive element, e.g. a prism for wavelength selection using a diffraction grating
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES USING STIMULATED EMISSION
    • H01S3/00Lasers, i.e. devices for generation, amplification, modulation, demodulation, or frequency-changing, using stimulated emission, of infra-red, visible, or ultra-violet waves
    • H01S3/10Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling a device placed within the cavity

Abstract

The invention relates to disposing a suppressor (160) in a resonant cavity present in a fiber laser (100), such as a Raman fiber laser (100). The suppressor can be effective in reducing the formation or buildup of energy at undesired wavelengths, such as undesired energy at higher order Raman Stokes shifts wavelengths.

Description

FIBER LASER HAVING A SUPPRESSOR

Technical Field

The invention relates to fiber lasers, and systems containing fiber lasers.

Background

One type of fiber laser is a Raman fiber laser. In general, Raman fiber lasers include a pump source coupled to a fiber, such as an optical fiber, having a gain medium with an active material. Energy emitted from the pump source at a certain wavelength λp, commonly referred to as the pump energy, is coupled into the fiber. As the pump energy interacts with the active material in the gain medium of the fiber, one or more Raman Stokes transitions can occur within the fiber, resulting in the formation of energy within the fiber at wavelengths corresponding to the Raman Stokes shifts that occur (e.g., λsi,

Typically, the fiber is designed so that the energy formed at one or more Raman Stokes shifts is substantially confined within the fiber. This can enhance the formation of energy within the fiber at one or more higher order Raman Stokes shifts. Often, the fiber is also designed so that at least a portion of the energy at wavelengths corresponding to predetermined, higher order Raman Stokes shifts (e.g., λsX, where x is equal to or greater than one) is allowed to exit the fiber.

Summary

In general, the invention relates to disposing a suppressor in a resonance cavity present in a fiber laser, such as a Raman fiber laser (e.g., a linear Raman fiber laser, a ring-shaped Raman fiber laser and/or a loop Raman fiber laser). The suppressor can be effective in reducing the formation or build up of energy at undesired wavelength(s), such as undesired energy at higher order Raman Stokes shifts wavelengths.

In one aspect, the invention features a fiber laser that includes an optical fiber containing a gain medium having an active material with a Stokes shift frequency (c/λr), where c is the speed of light. The optical fiber has a first end configured to receive energy at a wavelength λp. The optical fiber has N pairs of reflectors disposed therein. N is an integer having a value of at least one. Each of the N pairs of reflectors has an index. The index of each of the N pairs of reflectors is different than the index of the other pairs of reflectors. The optical fiber also has a suppressor disposed therein. The suppressor is configured to substantially suppress formation of energy at a wavelength (n+\), where λs(n+i)'' = V ~ (N+l)(λr":). For a pair of reflectors having an index with a value M, each reflector in the pair of reflectors is configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm, where λsm"1 = λp'1 - M(V')- M is an integer having a value of at least one and at most N.

The suppressor can be one or more long period gratings (e.g., having a resonance frequency of (c/λs(n+i)), where c is the speed of light).

In another aspect, the invention features a fiber laser system. The system includes an energy source configured to emit energy at a wavelength λp. The system also includes a fiber laser with an optical fiber containing a gain medium having an active material with a Stokes shift frequency 1- The optical fiber has a first end configured to receive energy at a wavelength λp. The optical fiber has N pairs of reflectors disposed therein. N is an integer having a value of at least one. Each of the N pairs of reflectors has an index. The index of each of the N pairs of reflectors is different than the index of the other pairs of reflectors. The optical fiber also has a suppressor disposed therein. The suppressor is configured to substantially suppress formation of energy at a wavelength λ^n+i), where λsoi+i) "1 = λp'1 - (N+lXλr*1)- For a pair of reflectors having an index with a value M, each reflector in the pair of reflectors is configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm, where λsm '1 = ' _ M( ')- M is an integer having a value of at least one and at most N. The energy source and the optical fiber are configured so that energy at emitted by the energy source at the wavelength λp can be coupled into the first end of the optical fiber.

The energy source can be a laser (e.g., a laser capable of lasing at λp).

In a further aspect, the invention features a fiber laser that includes an optical fiber containing a gain medium having an active material with a Stokes shift frequency V1- The optical fiber has a first end configured to receive energy at a wavelength λp. The fiber laser also includes N pairs of reflectors disposed in the optical fiber. N is an integer having a value of at least one. Each of the N pairs of reflectors has an index, and the index of each of the N pairs of reflectors is different than the index of the other pairs of reflectors. Each reflector in a pair of reflectors has an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm. M is an integer having a value of at least one and at most N and where λsm"1 = λp"1 - (M)(V'). The fiber laser further includes a suppressor disposed in the optical fiber. The suppressor is configured to substantially suppress formation of energy at a wavelength λs(n+i), where λs^+i)"1 = λp"1 ~ ( +1)(V')- The suppressor and N pairs of reflectors are configured so that during use power emitted by the optical fiber at the wavelength λsn is at least about 55% of power that enters the first end of the optical fiber at λp.

In a further aspect, the invention features a laser system. The system includes an energy source configured to emit energy at a wavelength λp. The system also includes a fiber laser having an optical fiber containing a gain medium with an active material with a Stokes shift frequency λ 1- The optical fiber has a first end configured to receive energy at a wavelength λp. The fiber laser also includes N pairs of reflectors disposed in the optical fiber. N is an integer having a value of at least one. Each of the N pairs of reflectors has an index, and the index of each of the N pairs of reflectors is different than -the-index of the-other pairs of reflectors^ -Each reflector in a-pair of reflectors has an _ index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm. M is an integer having a value of at least one and at most N and where λsm "1 = λp "1 - (M)(V'). The fiber laser further includes a suppressor disposed in the optical fiber. The suppressor is configured to substantially suppress formation of energy at a wavelength λs(n+i), where λs^+i)"1 = λp"1 - (N+1)(V')- The suppressor and N pairs of reflectors are configured so that during use power emitted by the optical fiber at the wavelength λs„ is at least about 55% of power that enters the first end of the optical fiber at λp. The energy source and the optical fiber are configured so that energy at emitted by the energy source at the wavelength λp can be coupled into the first end of the optical fiber. In one aspect, the invention features a fiber laser that includes an optical fiber containing a gain medium having an active material with a Stokes shift frequency λ 1. The optical fiber has a first end configured to receive energy at a wavelength λp. The fiber laser also includes N pairs of reflectors disposed in the optical fiber. N is an integer having a value of at least one. Each of the N pairs of reflectors has an index, and the index of each of the N pairs of reflectors is different than the index of the other pairs of reflectors. Each reflector in a pair of reflectors has an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm. M is an integer having a value of at least one and at most N and where λsm '' = λp"1 - (M)(V')- The fiber laser further includes a suppressor disposed in the optical fiber. The suppressor is configured to substantially suppress formation of energy at a wavelength λs(n+i), where = * ~ (N+IX 1)- The suppressor and N pairs of reflectors are configured so that during use power emitted by the optical fiber at wavelengths other than λsn is at most about 45% of power that enters the first end of the optical fiber at λp.

In another aspect, the invention features a laser system. The system includes an energy source configured to emit energy at a wavelength λp. The system also includes a -fitjerlaser havirrg-an optical-fiber-contaimng-a gain-medium with-an active material with a Stokes shift frequency V1. The optical fiber has a first end configured to receive energy at a wavelength λp. The fiber laser also includes N pairs of reflectors disposed in the optical fiber. N is an integer having a value of at least one. Each of the N pairs of reflectors has an index, and the index of each of the N pairs of reflectors is different than the index of the other pairs of reflectors. Each reflector in a pair of reflectors has an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm. M is an integer having a value of at least one and at most N and where λsm"1 = λp"1 - (MXV1)- The fiber laser further includes a suppressor disposed in the optical fiber. The suppressor is configured to substantially suppress formation of energy at a wavelength λ +i), where λs(n+i) "' = 1 ~~ (N+IXV1)- The suppressor and N pairs of reflectors are configured so that during use power emitted by the optical fiber at wavelengths other than λsn is at most about 45% of power that enters the first end of the optical fiber at λp. The energy source and the optical fiber are configured so that energy at emitted by the energy source at the wavelength λp can be coupled into the first end of the optical fiber.

In a further aspect, the invention features a fiber laser. The fiber laser includes an optical fiber containing a gain medium having an active material with a Stokes shift frequency . The optical fiber has a first end configured to receive energy at a wavelength λp. The fiber also includes N pairs of reflectors disposed in the optical fiber. N is an integer having a value of at least one. Each of the N pairs of reflectors has an index, and the index of each of the N pairs of reflectors is different than the index of the other pairs of reflectors. Each reflector in a pair of reflectors has an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm. M is an integer having a value of at least one and at most N and where λsm "1 = λp"1 - (M)(V')- The fiber laser further includes a suppressor disposed in the optical fiber. The suppressor is configured to substantially suppress formation of energy at a wavelength λs(n+i), where

In yet another aspect, the invention features a laser system. The system includes ~arrenergy~source-configured to-emifenergyat a-wavelength λp. The system also includes a fiber laser having an optical fiber containing a gain medium having an active material with a Stokes shift frequency 1- The optical fiber has a first end configured to receive energy at a wavelength λp. The fiber also includes N pairs of reflectors disposed in the optical fiber. N is an integer having a value of at least one. Each of the N pairs of reflectors has an index, and the index of each of the N pairs of reflectors is different than the index of the other pairs of reflectors. Each reflector in a pair of reflectors has an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm. M is an integer having a value of at least one and at most N and where λsm'1 = V - (M)(V ). The fiber laser further includes a suppressor disposed in the optical fiber. The suppressor is configured to substantially suppress formation of energy at a wavelength λs(n+i), where λs(n+i)" = V - (N+1)(V ). The energy source and the optical fiber are configured so that energy at emitted by the energy source at the wavelength λp can be coupled into the first end of the optical fiber.

In one aspect, the invention features a Raman fiber laser. The Raman fiber laser includes an optical fiber having a gain medium containing an active material with a Stokes shift frequency of 1. The optical fiber has a first end configured to receive energy at a wavelength λp. The optical fiber is configured so that the active material forms a resonance cavity in the gain medium for a wavelength λsn, where λsn '1 = λp"' _ (N)(V')- The Raman fiber laser also includes a suppressor disposed in the resonance cavity in the gain medium for the wavelength λsn. The suppressor is configured to substantially suppress formation of energy at a wavelength λs(n+i), where λs i+i)'1 = λp"' ~ (N+ 1)(V')- N is an integer having a value of at least one.

In some embodiments, the invention can provide a Raman fiber laser having a relatively high output power at a desired wavelength (e.g., at least about 0.1 Watt, at least about 0.5 Watt, at least about one Watt, at least about 2 Watts, at least about 5 Watts, at least about 10 Watts). Such a Raman fiber laser can operate, for example, under conditions of relatively high pump power (e.g., at least about 0.1 Watt, at least about 0.5 Watt, at least about one-Watt, at least-about-2 Watts.-aHeast about-5 Watts, at least about 10 Watts).

In certain embodiments, the invention can provide a Raman fiber laser having a relatively low output power at one or more undesired wavelengths (e.g., less than about one Watt, less than about 0.5 Watt, less than about 0.1 Watt, less than about 0.05 Watt). Such a Raman fiber laser can operate, for example, under conditions of relatively high pump power (e.g., at least about 0.1 Watt, at least about 0.5 Watt, at least about one Watt, at least about 2 Watts, at least about 5 Watts, at least about 10 Watts).

In some embodiments, the invention can provide a Raman fiber laser that can convert energy entering the Raman fiber laser at a particular wavelength (e.g., a pump wavelength) to energy exiting the Raman fiber laser at a different wavelength (e.g., a desired wavelength) with relatively high efficiency (e.g., an efficiency of: at least about 35%>, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%), at least about 85%, at least about 90%, at least about 95%, at least about 98%).

In certain embodiments, the invention can provide a Raman fiber laser than can convert energy entering the Raman fiber laser at a particular wavelength (e.g., a pump wavelength) to energy exiting the Raman fiber laser at wavelengths other than a desired wavelength with relatively low efficiency (e.g., an efficiency of: at most about 45%, at most about 40%, at most about 35%, at most about 30%, at most about 25%, at most about 20%), at most about 15%, at most about 10%o, at most about 5%, at most about 2%).

The Raman fiber lasers can provide these properties when the difference between the pump energy and the output energy is any value (e.g., relatively small or relatively large). In some embodiments, the difference between the pump energy and the output energy can be relatively large (e.g., at least about 100 cm"1, at least about 200 cm'1, at least about 500 cm"1, at least about 1,000 cm"1, at least about 1,250 cm"1, at least about 1,500 cm"1, at least about 1,750 cm"1, at least about 2,000 cm'1).

A fiber laser can be, for example, a Raman fiber laser. A Raman fiber laser can be, for example, a linear Raman fiber laser, ring-shaped Raman fiber laser or a loop (e.g., Sagnac loop) Raman fiber laser.

Features, objects and advantages of the invention are in the description, drawings and claims.

Description of Drawings

Fig. 1 is a schematic representation of an embodiment of a Raman fiber laser system;

Fig. 2 is a schematic representation of an embodiment of a Raman fiber laser system;

Fig. 3 is a schematic representation of an embodiment of a Raman fiber laser system;

Fig. 4 is a schematic representation of an embodiment of a Raman fiber laser system

Fig. 5 is a schematic representation of an embodiment of a Raman fiber laser system; Fig. 6 is a schematic representation of an embodiment of a Raman fiber laser system; and

Fig. 7 is a schematic representation of an embodiment of a Raman fiber laser system.

Detailed Description

Fig. 1 shows an embodiment of a Raman fiber laser system 100 including an optical fiber 110 and a laser 115. Laser 115 is configured so that energy emitted by laser 115 at a wavelength λp is coupled into optical fiber 110. Optical fiber 110 has a gain medium containing an active material (e.g., GeO2, P2O5, SiO2, B2O , SiOxFy or the like).

Optical fiber 110 includes a first pair of reflectors 120 and 130 (e.g., a pair of fiber Bragg gratings). Reflectors 120 and 130 are designed to reflect substantially all (e.g., about 100%) energy impinging thereon at a wavelength λsi, where λsi'1= λp "1 - \ (c/λr) is the Raman Stokes shift frequency for the active material in gain medium of fiber 110, and c is the speed of light.

Optical fiber 110 also includes a second pair of reflectors 140 and 150 (e.g., a pair of fiber Bragg gratings). Reflector 140 is designed to reflect substantially all (e.g., about 100%>) energy impinging thereon at wavelength λs2, and reflector 150 is designed to reflect a portion (e.g., less than about 98%, less than about- 95%^ less than about 90%, less than about 80%>, less than about 70%, less than 60%, less than about 50%, less than about 40%), less than about 30%, less than about 20%, less than about 10%>) of energy impinging thereon at wavelength λs2, where λs2 '1 = λsi"1 - λ 1-

Optical fiber 110 further includes a suppressor 160. Suppressor 160 is designed to suppress (e.g., substantially eliminate) the formation of energy at undesired higher order Raman Stokes shifts in fiber 110 (e.g., energy at λsn, where n is an integer having a value greater than 2, and λsn"1 = λs^.i)"1 - V1)-

With this arrangement, as energy at λp enters optical fiber 110, the energy at λp propagates through fiber 110 and interacts with the active material in the gain medium of fiber 110 to create energy at wavelength λsi. Energy at λsi propagates through fiber 110 in the forward direction until it reaches reflector 130 where it is reflected backward. Energy at λsi propagates through fiber 110 in the reverse direction until it reaches reflector 120 where it is reflected and then propagates through fiber 110 in the forward direction. Energy at λsi continues to propagate in fiber 110 in the forward in reverse directions between reflectors 120 and 130.

As energy at λsi propagates through fiber 110, it interacts with the active material in the gain medium of fiber 110 to create energy at wavelength λs2. Energy at λ^ propagating in fiber 110 in the reverse direction is reflected by reflector 140 and then propagates through fiber 110 in the forward direction. Energy at λs2 propagating through fiber 110 in the forward direction impinges on reflector 150. Some of the energy at λs2 impinging on reflector 150 is reflected by reflector 150 and then propagates through fiber 110 in the reverse direction, and some of the energy at λs2 impinging on reflector 150 passes through reflector 150 and exits fiber 110.

As energy at wavelength λs2 propagates through fiber 110, it can impinge upon suppressor 160, which reduces (e.g., substantially eliminates) the transfer of energy at wavelength λs2 to energy at wavelength λj (and/or energy at higher order Raman Stokes shifts for the active material in gain medium of fiber 110). In some embodiments, suppressor 160 is a long period grating (LPG) having a resonance frequency of (c/λs3), where λs3 '1 = λs2 '1 - 1- The LPG can couple energy impinging thereon at wavelength λj3 out of the gain medium of fiber 110 (e.g., into the cladding of fiber 110, which can be formed of a material, such as fused silica, that dissipates energy at λs3 relatively quickly). This can suppress the power at wavelength λs3 propagating in fiber 110, which correspondingly can suppress the formation of energy at higher order Raman Stokes shifts propagating in fiber 110. This can result in fiber 110 having a high power at wavelength λj2 propagating therein relative to a substantially similar system without suppressor 160.

Without wishing to be bound by theory, it is believed that the enhanced power at λs2 propagating in fiber 110 can be explained as follows. In general, it is believed that the stimulated Raman process at the wavelength λs is based on the general formula:

where 1^ , Is^ and Is^ represent the intensity of energy propagating in fiber 110 at wavelengths λsn, λs n-1), and λs(n+i), respectively, where:

λsn = λp - Nλr ; λs(n-i) = λp - (n-l)V ; λs vH)" - λp"' - (n-r-l)V1 ; and n is an integer having a value greater than or equal to one.

z is the dimension along the length of fiber 110 in the direction that the energy propagates therethrough, g is the Raman gain coefficient for energy propagating in fiber 110 at wavelength λsn, (e g-, due to gain in power at λsn in fiber 110 as energy is transferred from wavelength λs(n-i) to wavelength λsn via stimulated Raman scattering), α is the loss coefficient for energy propagating in fiber 110 at wavelength λsn due to, for example, imperfections, scattering and/or splicing in fiber 110.

The term - gls Is + describes the loss of intensity for energy propagating in fiber 110 at wavelength λsn due to transfer of energy (via Raman scattering) from wavelength λsn to energy at wavelength λs(n+i). It is believed that the term - gls s^ can be significant under certain circumstances, such as, for example, when Is is relatively large (e.g., at least about 0.05 Watt, at least about 0.1 Watt, at least about 0.5 Watt).

It is also believed that the loss of power at wavelength λsn propagating in fiber 110 will increase (e.g., nonlinearly increase) with the increase of the power at wavelength λs(n+i) propagating in fiber 110 as described by the following equation:

where g is the Raman gain coefficient for energy propagating in fiber 110 at wavelength λs(n+i) (e.g., due to gain in power at λs(n+i) in fiber 110 as energy is transferred from wavelength λs(n) to wavelength λs(n+i) via stimulated Raman scattering), β is the loss coefficient for energy propagating in fiber 110 at wavelength λs(n+i) due to, for example, imperfections, scattering and/or splicing in fiber 110.

It is further believed that the formation and/or build-up of Is can be reduced by increasing β . This can be achieved, for example, by using suppressor 160. As an example, suppressor 160 can be an LPG with a resonance frequency of (c/λs(n+i)). In certain embodiments, the bandwidth of suppressor 160 (e.g., an LPG) is narrow enough to avoid introduction of extra losses for energy at wavelengths other than λs(n+i). For example, the bandwidth of suppressor 160 can be less than about 60 nanometers (e.g., less than about 50 nanometers, less than about 30 nanometers, less than about five nanometers).

Fig. 2 shows a Raman fiber laser system 200 in which optical fiber 210 includes pairs of reflectors 120 and 130, and 140 and 155, and also includes a pair of gratings 170 and 180 (e.g., a pair of fiber Bragg gratings). Reflector 155 (e.g., a fiber Bragg grating) is designed to reflect substantially all (e.g., about 100%>) energy at λs2. Reflector 170 is designed to reflect substantially all (e.g., about 100%) energy at wavelength λs , and reflector 180 is designed to reflect a portion (e.g., less than about 98%, less than about 95%, less than about 90%, less than about 80%, less than about 70%, less than 60%, less than about 50%, less than about 40%, less than about 30%, less than about 20%, less than about 10%)) of energy at wavelength λs3.

Optical fiber 210 includes a suppressor 220. Suppressor 220 is designed to suppress (e.g., substantially eliminate) the formation of energy at undesired higher order Raman Stokes shifts in fiber 210 (e.g., energy at λsn, where n is an integer having a value greater than 3).

With this arrangement, as energy at λp enters optical fiber 210, the energy at λp propagates through fiber 210 and interacts with the active material in the gain medium of fiber 210 to create energy at wavelength λsi. Energy at λsi propagates in fiber 210 in the forward in reverse directions between reflectors 120 and 130.

As energy at λsi propagates through fiber 210, it interacts with the active material in the gain medium of fiber 210 to create energy at wavelength λs2. Energy at λs2 propagates through fiber 210 in the forward direction until it reaches reflector 155 where it is reflected backward. Energy at λs2 propagates through fiber 210 in the reverse direction until it reaches reflector 140 where it is reflected and then propagates through fiber 210 in the forward direction. Energy at λs2 continues to propagate in fiber 210 in the forward in reverse directions between reflectors 140 and 155.

As energy at λj2 propagates through fiber 210, it interacts with the active material in the gain medium of fiber 210 to create energy at wavelength λs3. Energy at λs propagating in fiber 210 in the reverse direction is reflected by reflector 170 and then propagates through fiber 210 in the forward direction. Energy at λj propagating through fiber 210 in the forward direction impinges on reflector 180. Some of the energy at λs3 impinging on reflector 180 is reflected by reflector 180 and then propagates through fiber 210 in the reverse direction, and some of the energy at λs3 impinging on reflector 180 passes through reflector 180 and exits fiber 210.

As energy at wavelength λs propagates through fiber 210, it can impinge upon suppressor 220, which reduces (e.g., substantially eliminates) the transfer of energy at wavelength λs3 to energy at wavelength λs4 (and/or energy at higher order Raman Stokes shifts for the active material in gain medium of fiber 110). In some embodiments, suppressor 220 is an LPG having a resonance frequency of (c/λs4), where λs4 ''= λs3 "' - λ 1 • The suppression of the power at wavelength λs4 propagating in fiber 210 can suppress the formation of energy at higher order Raman Stokes shifts propagating in fiber 210. This can result in fiber 210 having a high power at wavelength λs3 propagating therein relative to a substantially similar system without suppressor 210.

Fig. 3 shows a Raman fiber laser system 300 in which optical fiber 310 includes a pair of reflectors 120 and 135. Reflector 135 (e.g., a fiber Bragg grating) is designed to reflect a portion (e.g., less than about 98%, less than about 95%, less than about 90%, less than about 80%, less than about 70%, less than 60%, less than about 50%>, less than about 40%, less than about 30%, less than about 20%, less than about 10%) of energy impinging thereon at λsi.

Optical fiber 310 includes a suppressor 320. Suppressor 320 is designed to suppress (e.g., substantially eliminate) the formation of energy at undesired higher order Raman Stokes shifts in fiber 310 (e.g., energy at λsn, where n is an integer having a value greater than 1).

With this arrangement, as energy at λp enters optical fiber 310, the energy at λp propagates through fiber 310 and interacts with the active material in the gain medium of fiber 310 to create energy at wavelength λsi. Energy at wavelength λsi propagating in fiber 310 in the reverse direction is reflected by reflector 120 and then propagates through fiber 310 in the forward direction. Energy at λsι propagating through fiber 310 in the forward direction impinges on reflector 135.- Some of the energy at λsi impinging on reflector 135 is reflected by reflector 135 and then propagates through fiber 310 in the reverse direction, and some of the energy at λsi impinging on reflector 135 passes through reflector 135 and exits fiber 135.

As energy at wavelength λsi propagates through fiber 310, it can impinge upon suppressor 320, which reduces (e.g., substantially eliminates) the transfer of energy at wavelength λsi to energy at wavelength λs2 (and/or energy at higher order Raman Stokes shifts for the active material in gain medium of fiber 310). In some embodiments, suppressor 320 is an LPG having a resonance frequency of (c/λs2). The suppression of the power at wavelength λs2 propagating in fiber 310 can suppress the formation of energy at higher order Raman Stokes shifts propagating in fiber 310. This can result in fiber 310 having a high power at wavelength λsi propagating therein relative to a substantially similar system without suppressor 310.

While Raman fiber lasers and Raman fiber laser systems have been described in which an optical fiber contains, one, two or three pairs of reflectors and a suppressor, the invention is not limited to these embodiments. More generally, the optical fiber can have N pairs of reflectors (e.g., pairs of fiber Bragg gratings) disposed therein, where N is an integer having a value of at least one (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc). For a Raman fiber laser or Raman fiber laser system in which the optical fiber has N pairs of reflectors disposed therein, the optical fiber also includes a suppressor designed to suppress (e.g., substantially eliminate) the formation of energy at undesired higher order Raman Stokes shifts in the optical fiber (e.g., energy at λs(n+i)). In general, for (N-l) of the pairs of reflectors, each pair of reflectors is designed to reflect substantially all (e.g., about 100%) energy impinging at corresponding a corresponding wavelength λsm, where M is an integer having a value of from one to (N- 1)) (i.e., each of these pairs of reflectors is designed to reflect energy at a different wavelength λsm, where M is an index that differs for each pair of reflector, and M = 1 ...(N-l)). For the Nth other pair of reflectors, one reflector (e.g., the reflector of the Nth pair of reflectors that is closer to the end of optical fiber configured to received energy at wavelength λp) is designed to reflect substantially all energy at wavelength λsn, and the other reflector (e.g., the reflector of the Nth pair of reflectors that is further from the end of optical fiber configured to received energy at wavelength λp) is designed to reflect a portion (e.g., less than about 98%, less than about 95%, less than about 90%, less than about 80%), less than about 70%, less than 60%), less than about 50%>, less than about 40%), less than about 30%>, less than about 20%>, less than about 10%>) of energy impinging thereon at λsn.

In some embodiments, the N pairs of reflectors are nested (Fig. 4). The invention is not limited to such embodiments, however. Generally, the pairs of reflectors can be disposed in an optical fiber in any manner. Typically, the reflectors are disposed within the optical fiber so that, when traveling along the optical fiber from starting at one end of the optical fiber and moving toward the other end of the optical fiber, a reflector from each of the N pairs of reflectors is encountered before encountering the second reflector from any of the N pairs of reflectors. For example, in system 100, the positions of reflectors 130 and 150 can be switched. As another example, in system 200, the positions of reflectors 180, 155 and/or 130 can be switched.

Fig. 5 shows an embodiment of a ring-shaped Raman fiber laser system 500. System 500 includes an optical fiber 510. System 500 also includes a ring cavity 520 formed of an optical fiber having an active material. A wavelength division multiplexer (WDM) 530 couples energy between fibers 510 and 520. Fiber 510 includes a reflector 540 and a reflector 550, and fiber 520 includes a reflector 560 and a suppressor 570.

Reflectors 540 and 560 are designed to reflect substantially all (e.g., about 100%) of energy impinging thereon at the wavelength λs2. Reflector 550 is designed to reflect substantially all (e.g., 100%) energy impinging thereon at the wavelength λp. For example, reflectors 540, 550 and 560 can be in the form of fiber Bragg gratings.

Suppressor 570 is designed to suppress (e.g., substantially eliminate) the formation of energy at higher order Raman Stokes shifts in fiber 520 (e.g., at the wavelength λj ). Suppressor 570 can be, for example, an LPG having a resonance frequency of c/λs .

With this arrangement, energy at λp enters fiber 510, goes through WDM 530 into fiber 520, exits fiber 520 via WDM 530 and re-enters fiber 510. Energy at λp then propagates in the forward direction in fiber 510 and impinges upon reflector 550 where it is reflected backward. This backward reflected energy can then be transferred into fiber 520 via WDM 530. Thus, energy at wavelength λp propagates through fiber 520 in the forward and in the reverse directions.

As energy at wavelength λp propagates through fiber 520, it interacts with the gain medium in fiber 520 to form energy at λsi, propagating through fiber 520 in the forward and in the reverse directions. WDM 530 is designed so that substantially no energy propagating in fiber 520 at the wavelength λsi can escape fiber 520.

As energy at wavelength λsi propagates through fiber 520, it interacts with the "gain medium in fiber 520 to-fornrenergy-at λ 2 propagating through fiber 520 in the forward and in the reverse directions. WDM 530 is designed so that energy propagating in fiber 520 at the wavelength λs2 can be transferred to fiber 510 and vice-versa, and a portion of the energy at the wavelength λs2 propagating in fibers 510 and 520 is reflected between reflectors 540 and 560. A portion of the energy in fibers 510 and 520 propagates along fiber 510 and exits fiber 510 at the opposite end from where energy at λp enters fiber 510.

Suppressor 570 reduces (e.g., substantially eliminates) the formation of energy at undesired higher order Stokes shifts (e.g., λs3, λs , λs5, etc.). Thus, a resonance cavity for energy at the wavelength λs2 is formed in system 500 by reflectors 540 and 560 and suppressor 570 is disposed in the resonance cavity.

While Fig. 5 has shown a ring-shaped Raman fiber system having one ring resonator, those skilled in the art will understand that the concept can be applied to ring- shaped Raman fiber laser systems having multiple ring resonators (e.g., two ring resonators, three ring resonators, four ring resonators, five ring resonators, six ring resonators, seven ring resonators, eight ring resonators, nine ring resonators, 10 ring resonators, etc.). In general, for a ring-shaped Raman fiber system having N ring resonators, the Nth ring resonator can have a suppressor disposed therein that is designed to reduce (e.g., substantially eliminate) the formation of energy in the optical fiber at an undesired higher order Stokes shifts (e.g., λs(n+i)). In certain embodiments, multiple WDMs can be used.

Those skilled in the art will understand that one or more appropriate suppressors can also be used in ring-shaped Raman fiber laser systems that are cascaded.

Fig. 6 shows a loop Raman fiber laser system 600 having optical fibers 610, 620 and 660, optical circulators 630 and 640, a suppressor 650 and a reflector (e.g., a fiber Bragg grating) 670. Energy at the wavelength λp enters fiber 620 via optical circulator 630 (e.g., a left hand optical circulator). As energy at the wavelength λp propagates through fiber 620, it interacts with the active material in the gain medium of fiber 620 to form energy at wavelength λsi. Suppressor 650 is designed to reduce (e.g., substantially eliminate) the formation of energy at undesired higher order Stokes shifts (e.g., λS2). Εnergy at~ sT exits fiber 620 via optical circulator 640 and enters fiber 660, where energy at wavelength λsi impinges on reflector 670. Reflector 670 reflects a portion of this energy back to circulator 640, and then into fiber 620. The energy at wavelength λsi that is not reflected by reflector 670 can exit system 600 via fiber 660 as shown.

While Fig. 6 has shown a loop Raman fiber system having one resonator, those skilled in the art will understand that the concept can be applied to loop Raman fiber laser systems having more than one ring resonator (e.g., two resonators, three resonators, four resonators, five resonators, six resonators, seven resonators, eight resonators, nine resonators, 10 resonators, etc.). In general, for a ring-shaped Raman fiber system having N resonators, the Nth resonator can have a suppressor disposed therein that is designed to reduce (e.g., substantially eliminate) the formation of energy in the optical fiber at an undesired higher order Stokes shifts (e.g., λs(n+i)). Those skilled in the will understand that one or more appropriate suppressors can also be used in loop Raman fiber laser systems that are cascaded.

While certain embodiments have been described, the invention is not limited to these embodiments. For example, the reflectors need not be in the form of fiber Bragg gratings. For example, one or more of the reflectors can be a loop mirror, or one or more reflectors can be in the form of a coated mirror (e.g., a coated mirror at one or both ends of a section of optical fiber). As another example, the suppressor(s) need not be in the form of LPG(s). For example, one or more of the suppressors can be in the form of gratings (e.g., short period gratings) that are substantially nonperpendicular to the length of the fiber along which energy propagates. In these embodiments, the gratings of the suppressor can be selected to scatter one or more wavelengths of interest (e.g., one or more higher order Raman Stokes shift wavelengths). As an additional example, the type of laser used can be varied. Examples of lasers that can be used include semiconductor diode lasers (e.g., high power semiconductor diode lasers) and double clad doped fiber lasers. As a further example, various types of optical fibers can be used, including, for example, double clad optical fibers and polarization maintaining optical fibers. The materials from which the optical fiber(s) are formed can also be varied, generally depending upon the intended-use.— As-yet another example, the relative and/or absolute lengths of one or more of the sections of the optical fiber can be varied based upon the intended use of the Raman fiber laser.

Moreover, while the fibers and systems have been described as Raman fiber lasers and Raman fiber laser systems, those skilled in the art will appreciate that the general concepts described can be extended to provide amplifiers and amplifier systems. Generally, a fiber amplifier provides gain for energy at a wavelength of interest without the use of a lasing cavity (e.g., without a resonator and/or operating below lasing threshold). Fig. 7 is a schematic view of an embodiment of a fiber amplifier system 500 in which fiber 1500 is used as a signal amplifier. Fiber 1500 contains one or more suppressors (e.g., as described above but without reflector(s)). An input signal enters system 1400 via fiber 1101. Energy source 1201 emits a pump signal 1301. The input signal in fiber 1101 and pump signal 1301 are coupled into fiber 1500 via coupler 1401. Such couplers are known to those skilled in the art. Pump signal 1301 interacts with the active material(s) in the sections of fiber 1500, and the input signal is amplified. A device 1900 (e.g., an isolator) separates the amplified input signal from the pump signal so that the pump signal travels along fiber 1800, and the amplified input signal travels along fiber 1950. While Fig. 7 shows one embodiment of fiber 1500 in a fiber amplifier system, other fiber amplifier systems in which fiber 1500 can be used will be apparent to those of skill in the art.

Additional examples of systems containing one or more suppressors are disclosed in commonly owned U.S. Patent Serial No. , filed on even date herewith, and entitled "Optical Fiber and System Containing Same," which is hereby incoφorated by reference.

Furthermore, while the foregoing discussion has focused on lasers having an optical gain medium formed of one active material, those skilled in the art will understand that the concepts can be applied to fiber lasers (e.g., Raman fiber lasers, such as linear Raman fiber lasers, ring-shaped Raman fiber lasers, loop Raman fiber lasers and the like) having more than one active material in the gain medium. In such a system where i is the number of active materials in the gain medium,

In addition, the systems can be configured, for example, for side pumping and/or end pumping.

Moreover, while certain positions have been shown for components (e.g., reflectors and/or a suppressor) in fiber laser systems, those skilled in the art will understand that other positions can be used for these components. In general, however, the reflectors and suppressor should be disposed so that the suppressor is disposed within the resonator cavity of interest. Thus, for example, in system 100 (Fig. 1), the ordering of components from left to right in the figure can be reflector 140, reflector 120, reflector 130, suppressor 160 and reflector 150. As another example, the ordering of components in system 100 from left to right can be reflector 140, suppressor 160, reflector 120, reflector 130 and reflector 150. Other arrangements can also be used. Other embodiments are in the claims. What is claimed is:

Claims

Claims
1. A fiber laser, comprising: an optical fiber containing a gain medium having an active material with a Stokes shift frequency λ , the optical fiber having a first end configured to receive energy at a wavelength λp;
N pairs of reflectors disposed in the optical fiber, N being an integer having a value of at least one, each of the N pairs of reflectors having an index, the index of each of the N pairs of reflectors being different than the index of the other pairs of reflectors; and a suppressor disposed in the optical fiber, the suppressor being configured to substantially suppress formation of energy at a wavelength λs(n+i), where
λ ^ ' - N+iX 1),
and wherein for a pair of reflectors having an index with a value M, each reflector in the pair of reflectors having the index with the value M is configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm, where
λsm'^ ' - M 1),
and M is an integer having a value of at least one and at most N.
2. The fiber laser of claim 1 , wherein the suppressor comprises one or more long period gratings.
3. The fiber laser of claim 2, wherein the one or more long period gratings have a resonance frequency of (c/λs(n+i)), where c is the speed of light. '
4. The fiber laser of claim 1, wherein each of the N pairs of reflectors has a first reflector and a second reflector, and the suppressor is disposed between the first and second reflectors in each of the N pairs of reflectors.
5. The fiber laser of claim 4, wherein the first reflector in each of the N pairs of reflectors is disposed in the optical fiber in a position along the optical fiber that is closer to the first end of the optical fiber than the second reflector in any of the N pairs of reflectors.
6. The fiber laser of claim 1 , wherein each of the N pairs of reflectors has a first reflector and a second reflector, and the first reflector in each of the N pairs of reflectors is disposed in the optical fiber in a position along the optical fiber that is closer to the first end of the optical fiber than the second reflector in any of the N pairs of reflectors.
7. The fiber laser of claim 1 , wherein N is one.
8. The fiber laser of claim 7, wherein the pair of reflectors includes first and second reflectors, the first reflector being configured to reflect substantially all energy impinging thereon at λsi.
9. The fiber laser of claim 8, wherein the second reflector is configured to reflect less than about 98% of energy impinging thereon at λsi.
10. The fiber laser of claim 8, wherein the first reflector is disposed in the optical fiber in a position along the optical fiber that is closer to the first end of the optical fiber than the second reflector.
11. The fiber laser of claim 8, wherein the suppressor is disposed between the first and second reflectors.
12. The fiber laser of claim 8, wherein the suppressor comprises one or more long period gratings having a resonance frequency of (c/λs2), where c is the speed of light.
13. The fiber laser of claim 1, wherein N is two.
14. The fiber laser of claim 13, wherein a first pair of reflectors is configured to reflect substantially all energy impinging thereon at λsi.
15. The fiber laser of claim 14, wherein a second pair of reflectors includes first and second reflectors, the first reflector being configured to reflect substantially all energy impinging thereon at λs2-
16. The fiber laser of claim 15, wherein the second reflector is configured to reflect less than about 98% of energy impinging thereon at λs2.
17. The fiber laser of claim 15, wherein the first reflector is disposed in the "optical fiber in a Dosition along he optical fiber that is closer to the first end of the optical fiber than the second reflector.
18. The fiber laser of claim 15, wherein the suppressor is disposed between the first and second reflectors.
19. The fiber laser of claim 15, wherein the suppressor comprises one or more long period gratings having a resonance frequency of (c/λs ), where c is the speed of light.
20. The fiber laser of claim 1 , wherein N is three.
21. The fiber laser of claim 20, wherein a first pair of reflectors is configured to reflect substantially all energy impinging thereon at λsi.
22. The fiber laser of claim 21, wherein a second pair of reflectors is configured to reflect substantially all energy impinging thereon at λs2.
23. The fiber laser of claim 22, wherein a third pair of reflectors includes first and second reflectors, the first reflector being configured to reflect substantially all energy impinging thereon at λj .
24. The fiber laser of claim 23, wherein the second reflector is configured to reflect less than about 98%) of energy impinging thereon at λs .
25. The fiber laser of claim 23, wherein the first reflector is disposed in the optical fiber in a position along the optical fiber that is closer to the first end of the optical fiber than the second reflector.
26. The fiber laser of claim 23, wherein the suppressor is disposed between the first and second reflectors.
27. The fiber laser of claim 23, wherein the suppressor comprises one or more long period gratings having a resonance frequency of (c/λs4), where c is the speed of light.
28. The fiber laser of claim 1, wherein N is four.
29. The fiber laser of claim 28, wherein a first pair of reflectors is configured to reflect substantially all energy impinging thereon at λsi.
30. The fiber laser of claim 29, wherein a second pair of reflectors is configured to reflect substantially all energy impinging thereon at λs2-
31. The fiber laser of claim 30, wherein a third pair of reflectors is configured to reflect substantially all energy impinging thereon at λs .
32. The fiber laser of claim 22, wherein a fourth pair of reflectors includes first and second reflectors, the first reflector being configured to reflect substantially all energy impinging thereon at λj4.
33. The fiber laser of claim 32, wherein the second reflector is configured to reflect less than about 98%) of energy impinging thereon at λs4.
34. The fiber laser of claim 32, wherein the first reflector is disposed in the optical fiber in a position along the optical fiber that is closer to the first end of the optical fiber than the second reflector.
35. The fiber laser of claim 32, wherein the suppressor is disposed between the first and second reflectors.
36. The-fiber aser of claiπr32, wherein the suppressor comprises one or more long period gratings having a resonance frequency of (c/λs5), where c is the speed of light.
37. The fiber laser of claim 1 , wherein N is five.
38. The fiber laser of claim 37, wherein a first pair of reflectors is configured to reflect substantially all energy impinging thereon at λsi.
39. The fiber laser of claim 38, wherein a second pair of reflectors is configured to reflect substantially all energy impinging thereon at λs2.
40. The fiber laser of claim 39, wherein a third pair of reflectors is configured to reflect substantially all energy impinging thereon at λs .
41. The fiber laser of claim 40, wherein a fourth pair of reflectors is configured to reflect substantially all energy impinging thereon at λs4.
42. The fiber laser of claim 41, wherein a fifth pair of reflectors includes first and second reflectors, the first reflector being configured to reflect substantially all energy impinging thereon at λj5.
43. The fiber laser of claim 42, wherein the second reflector is configured to reflect less than about 98%> of energy impinging thereon at λs5.
44. The fiber laser of claim 42, wherein the first reflector is disposed in the optical fiber in a position along the optical fiber that is closer to the first end of the optical fiber than the second reflector.
45. The fiber laser of claim 42, wherein the suppressor is disposed between the first and second reflectors.
46. The fiber laser of claim 42, wherein the suppressor comprises one or more long period gratings having a resonance frequency of (c/λsδ), where c is the speed of light.
47. The fiber laser of claim 1 , wherein N is six.
48. The fiber laser of claim 1 , wherein N is seven.
49. The fiber laser of claim 1 , wherein N is eight.
50. The fiber laser of claim 1 , wherein N is nine.
51. The fiber laser of claim 1, wherein N is 10.
52. The fiber laser of claim 1, wherein N is greater than 10.
53. The fiber laser of claim 1, wherein the active material comprises a material selected from the group consisting of GeO2, P2O5, SiO2, B2O3 and SiOxFy.
54. The fiber laser of claim 1 , wherein the active material comprises GeO2.
55. The fiber laser of claim 1 , wherein the active material comprises P2O5.
56. The fiber laser of claim 1 , wherein the suppressor has a bandwidth of at most about 60 nanometers.
57. The fiber laser of claim 1 , wherein the suppressor and N pairs of reflectors are configured so that during use a power emitted by the optical fiber at λsn is at least about 55%» of a power that enters the first end of the optical fiber at λp.
58. The fiber laser of claim 57, wherein the suppressor and N pairs of reflectors are configured so that during use a total power emitted by the optical fiber at wavelengths other than λsn is at most about 45%> of power that enters the first end of the optical fiber at λp.
59. The fiber laser of claim 1, wherein the suppressor and N pairs of reflectors are configured so that during use a total power emitted by the optical fiber at wavelengths other than λ is at most about 45% of a power that enters the first end of the optical fiber at λp.
60. A fiber laser system, comprising: an energy source configured to emit energy at a wavelength λp; and a fiber laser, comprising: an optical fiber containing a gain medium having an active material with a Stokes shift frequency λ 1, the optical fiber having a first end configured to receive energy at a wavelength λpj
N pairs of reflectors disposed in the optical fiber, N being an integer having a value of at least one, each of the N pairs of reflectors having an index, the index of each of the N pairs of reflectors being different than the index of the other pairs of reflectors; and a suppressor disposed in the optical fiber, the suppressor being configured to substantially suppress formation of energy at a wavelength λs(n+i), where
and wherein for a pair of reflectors having an index with a value M, each reflector in the pair of reflectors having the index with the value M is configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm, where
λsm-^ ' - M 1),
and M is an integer having a value of at least one and at most N, the energy source and the optical fiber being configured so that energy at emitted by the energy source at the wavelength λp can be coupled into the first end of the optical fiber.
61. The system of claim 60, wherein the energy source comprises a laser.
62. The system of claim 61, wherein the energy sources is capable of lasing at λp.
63. A fiber laser, comprising: an optical fiber containing a gain medium having an active material with a Stokes shift frequency λ , the optical fiber having a first end configured to receive energy at a wavelength λpj
N pairs of reflectors disposed in the optical fiber, N being an integer having a value of at least one, each of the N pairs of reflectors having an index, the index of each of the N pairs of reflectors being different than the index of the other pairs of reflectors, each reflector in a pair of reflectors having an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm, where M is an integer having a value of at least one and at most N and where
a suppressor disposed in the optical fiber, the suppressor being configured to substantially suppress formation of energy at a wavelength λs(n+i), where
wherein the suppressor and N pairs of reflectors are configured so that during use power emitted by the optical fiber at λsn is at least about 55% of power that enters the first end of the optical fiber at λp.
64. The fiber laser of claim 63, wherein the suppressor and N pairs of reflectors are configured so that during use at least a total power emitted by the optical fiber at wavelengths other than λsn is at most about 45% of power that enters the first end of the optical fiber at λp.
65. A fiber laser system, comprising: an energy source configured to emit energy at a wavelength λp; and a fiber laser, comprising: an optical fiber containing a gain medium having an active material with a Stokes shift frequency λ 1, the optical fiber having a first end configured to receive energy at a wavelength λp;
N pairs of reflectors disposed in the optical fiber, N being an integer having a value of at least one, each of the N pairs of reflectors having an index, the index of each of the N pairs of reflectors being different than the index of the other pairs of reflectors, each reflector in a pair of reflectors having an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm, where M is an integer having a value of at least one and at most N and where
λsm "1 = V1 - (MXV1); and
a suppressor disposed in the optical fiber, the suppressor being configured to substantially suppress formation of energy at a wavelength λs(n+i), where
wherein the suppressor and N pairs of reflectors are configured so that during use power emitted by the optical fiber at λsn is at least about 55%> of power that enters the first end of the optical fiber at λp, and the energy source and the optical fiber are configured so that energy at emitted by the energy source at the wavelength λp can be coupled into the first end of the optical fiber.
66. The system of claim 65, wherein the energy source comprises a laser.
67. The system of claim 66, wherein the energy sources is capable of lasing at λp.
68. A fiber laser, comprising: an optical fiber containing a gain medium having an active material with a Stokes shift frequency λ , the optical fiber having a first end configured to receive energy at a wavelength λp;
N pairs of reflectors disposed in the optical fiber, N being an integer having a value of at least one, each of the N pairs of reflectors having an index, the index of each of the N pairs of reflectors being different than the index of the other pairs of reflectors, each reflector in a pair of reflectors having an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm, where M is an integer having a value of at least one and at most N and where
λsm '1 = , - (MX 1); and
a suppressor disposed in the optical fiber, the suppressor being configured to substantially suppress formation of energy at a wavelength λ +i), where
λs(n+,) "1 = λp'1 - ( +υ(v1),
wherein the suppressor and N pairs of reflectors are configured so that during use at least a total power emitted by the optical fiber at wavelengths other λsn is at most about 45% of power that enters the first end of the optical fiber at λp.
69. A fiber laser system, comprising: an energy source configured to emit energy at a wavelength λp; and a fiber laser, comprising: an optical fiber containing a gain medium having an active material with a Stokes shift frequency λ 1, the optical fiber having a first end configured to receive energy at a wavelength λp;
N pairs of reflectors disposed in the optical fiber, N being an integer having a value of at least one, each of the N pairs of reflectors having an index, the index of each of the N pairs of reflectors being different than the index of the other pairs of reflectors, each reflector in a pair of reflectors having an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm, where M is an integer having a value of at least one and at most N and where
λsm-^ ' - MX 'X and
a suppressor disposed in the optical fiber, the suppressor being configured to substantially suppress formation of energy at a wavelength λs(n+i), where
wherein the suppressor and N pairs of reflectors are configured so that during use at least a total power emitted by the optical fiber at wavelengths other λsn is at most about 45%) of power that enters the first end of the optical fiber at λp, and the energy source and the optical fiber are configured so that energy at emitted by the energy source at the wavelength λp can be coupled into the first end of the optical fiber.
70. The system of claim 69, wherein the energy source comprises a laser.
71. The system of claim 70, wherein the energy sources is capable of lasing at λp.
72. A fiber laser, comprising: an optical fiber containing a gain medium having an active material with a Stokes shift frequency \ the optical fiber having a first end configured to receive energy at a wavelength λp;
N pairs of reflectors disposed in the optical fiber, N being an integer having a value of at least one, each of the N pairs of reflectors having an index, the index of each of the N pairs of reflectors being different than the index of the other pairs of reflectors, each reflector in a pair of reflectors having an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm, where M is an integer having a value of at least one and at most N and where
λsm "1 = V1 - (M)(V1); and
a suppressor disposed in the optical fiber, the suppressor being configured to substantially suppress formation of energy at a wavelength λs(n+i), where
73. A fiber laser system, comprising: an energy source configured to emit energy at a wavelength λp; and a fiber laser, comprising: an optical fiber containing a gain medium having an active material with a Stokes shift frequency V1, the optical fiber having a first end configured to receive energy at a wavelength λp;
N pairs of reflectors disposed in the optical fiber, N being an integer having a value of at least one, each of the N pairs of reflectors having an index, the index of each of the N pairs of reflectors being different than the index of the other pairs of reflectors, each reflector in a pair of reflectors having an index with a value M being configured to at least partially reflect energy at a wavelength λsm and to form a resonance cavity for energy at the wavelength λsm, where M is an integer having a value of at least one and at most N and where
λsm "1 = λp "1 - (M)(V1); and a suppressor disposed in the optical fiber, the suppressor being configured to substantially suppress formation of energy at a wavelength λs(n+i), where
and the energy source and the optical fiber are configured so that energy at emitted by the energy source at the wavelength λp can be coupled into the first end of the optical fiber.
75. A Raman fiber laser, comprising: an optical fiber having a gain medium containing an active material with a Stokes shift frequency of 1, the optical fiber having a first end configured to receive energy at a wavelength λp, the optical fiber being configured so that the active material forms a resonance cavity in the gain medium for a wavelength λsn, where
λ^ ' - CNXλ and
a suppressor disposed in the resonance cavity in the gain medium for the wavelength λsn, the suppressor being configured to substantially suppress formation of energy at a wavelength λs(n+i), where
wherein N is an integer having a value of at least one.
76. The Raman fiber laser of claim 75, wherein the optical fiber is configured so that the Raman fiber laser comprises a linear Raman fiber laser.
77. The Raman fiber laser of claim 75, wherein the optical fiber is configured so that the Raman fiber laser comprises a ring-shaped Raman fiber laser.
78. The Raman fiber laser of claim 75, wherein that optical fiber is configured so that the Raman fiber laser comprises a loop Raman fiber laser.
79. The Raman fiber laser of claim 78, wherein the loop Raman fiber laser comprises a Sagnac loop Raman fiber laser.
80. The Raman fiber laser of any of claims 75-78, wherein N is one.
81. The Raman fiber laser of any of claims 75-78, wherein N is two.
82. The Raman fiber laser of any of claims 75-78, wherein N is three.
83. The Raman fiber laser of any of claims 75-78, wherein N is four.
84. The Raman fiber laser of any of claims 75-78, wherein N is five.
85. The Raman fiber laser of any of claims 75-78, wherein N is six.
86. The Raman fiber laser of any of claims 75-78, wherein N is seven.
87. The Raman fiber laser of any of claims 75-78, wherein N is eight.
88. The Raman fiber laser of any of claims 75-78, wherein N is nine.
89. The Raman fiber laser of any of claims 75-78, wherein N is 10.
90. The fiber laser of any of claims 75-89, wherein the suppressor comprises one or more long period gratings.
91. The fiber laser of claim 90, wherein the one or more long period gratings have a resonance frequency of (cA*(n+o), where c is the speed of light.
92. The fiber laser of any of claims 75-91, wherein the active material is selected from the group consisting of GeO2, P2O5, SiO2 and B2θ .
93. The fiber laser of any of claims 75-91 , wherein the active material comprises Geθ2.
94. The fiber laser of any of claims 75-91, wherein the active material comprises P2O .
95. A Raman fiber laser system, comprising: an energy source configured to emit energy at a wavelength λp; and a Raman fiber laser, comprising: an optical fiber having a gain medium containing an active material with a Stokes shift frequency of λ 1, the optical fiber having a first end configured to receive energy at the wavelength λp, the optical fiber being configured so that the active material forms a resonance cavity in the gain medium for a wavelength λsn, where
λsn-^ ' - NXλ nd
a suppressor disposed in the resonance cavity in the gain medium for the wavelength λsn, the suppressor being configured to substantially suppress formation of energy at a wavelength λS(n+i), where
λs(n+.) = V ' - (N+IXV'X wherein N is an integer having a value of at least one, and the energy source and the optical fiber are configured so that energy at emitted by the energy source at the wavelength λp can be coupled into the first end of the optical fiber.
PCT/US2002/014926 2001-05-15 2002-05-13 Fiber laser having a suppressor WO2002093697A3 (en)

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