TECHNICAL FIELD

The technical field generally relates to a chirped pulse amplification system and more particularly concerns the use of a fixed bulk compressor in such a system.

BACKGROUND

Chirped pulse amplification (CPA) is a widely used technique to amplify light pulses to high energies, while mitigating the deleterious effects of nonlinearities. This is achieved by temporally spreading the pulse before amplification to reduce peak power, followed by post-amplification compression, resulting in a short, high energy pulse train.

A CPA system is thus composed of three main parts: a stretcher, an amplifying stage, and a compressor. When using a fiber-based amplifier, it is advantageous to use a stretcher which is also fiber-based, as it is simple to use and does not need to be aligned, aside from fiber splices.

However, at the output of the amplifier, a bulk compressor, often in the form of a Treacy grating pair, is necessary. This is because the light in such a compressor travels through little to no bulk material, with a relatively high beam diameter, reducing peak irradiance. This is significant, since peak power is maximized at the output of the compressor, and this is where light is most susceptible to nonlinear effects.

In a CPA system, the bulk compressor is often composed of disjoint optical elements that need to be individually aligned. Furthermore, the distance and/or angle between gratings need to be tunable, as minute adjustments are required to match the dispersive characteristics of the stretcher and other system components to optimize pulse duration. All those factors lead to a compressor that can be bulky and cumbersome to align.

In view of the above, there remains a need for compressor designs that eliminate at least some of the aforementioned drawbacks.

SUMMARY

In accordance with one aspect, there is provided a chirped pulse amplification system for amplifying optical pulses.

The chirped pulse amplification system includes a pulse stretcher comprising an optical fiber provided with a Fiber Bragg grating (FBG) having a dispersion profile designed to stretch each of the optical pulses into stretched optical pulses. The pulse stretcher further comprises a tuning mechanism coupled to the FBG for tuning the dispersion profile.

The chirped pulse amplification system further includes an amplifier receiving and amplifying the stretched optical pulses into amplified stretched optical pulses.

The chirped pulse amplification system also includes a bulk compressor provided downstream the amplifier for compressing the amplified stretched optical pulses into amplified compressed optical pulses. The bulk compressor comprises a mounting block made of solid material and defining a plurality of mounting surfaces. The bulk compressor further comprises a plurality of optical components performing the compressing and mounted on the mounting block in a fixed mutual spatial relationship. Each of the optical components is rigidly affixed to a respective one of the mounting surfaces.

In some implementations, the pulse stretcher comprises a circulator successively connecting an input port for receiving the input optical pulses, an FBG port connected to the optical fiber to direct the input optical pulses towards the FBG and receiving the stretched optical pulses, and an output port for directing the stretched optical pulses towards the amplifier. The FBG may have a chirped grating period.

In some implementations, the pulse stretcher comprises a tuning mechanism coupled to the FBG for tuning the dispersion profile of the FBG. The tuning mechanism may be configured to apply a temperature variation to the optical fiber which is non-uniform along the FBG, or a strain on the optical fiber which is non-uniform along the FBG.

In some implementations, the chirped pulse amplification system may further include a feedback loop controlling the tuning mechanism based on the amplified compressed optical pulses. The feedback loop may comprise a pulse measurement device disposed downstream the bulk compressor and configured to measure and analyse the amplified compressed optical pulses. The pulse measurement device may send a feedback signal to the tuning mechanism. The feedback loop may be configured to adjust the dispersion profile of the FBG of the pulse stretcher to compensate for at least one of misalignments or manufacturing errors of said system or nonlinear effects induced in the amplified stretched optical pulses by the amplifier.

In some implementations, the amplifier is a fiber amplifier.

In some implementations, the mounting block of the bulk compressor is a monolithic structure and may be made of a machinable and thermally stable material.

Each optical component of the bulk compressor may be one of a grating, a lens, or a mirror.

In some implementations, the optical components of the bulk compressor are mounted into a Treacy configuration. The bulk compressor may comprise an input receiving the amplified stretched optical pulses as an input beam, and the optical components of the bulk compressor may include a first grating angularly dispersing the input beam, a second grating spatially dispersing the input beam, and a pair of plane mirrors shifting and retro-reflecting the input beam for retro-propagation through the second grating and first grating. In some implementations, the pair of plan mirrors may be disposed in a rooftop configuration.

In some implementations, at least one of the mounting surfaces of the bulk compressor forms a collar surrounding a light passage, and the optical component affixed to this at least one of the mounting surfaces has a front face comprising a peripheral portion mounted in direct contact with said collar. The optical components may be glued to the mounting block from the side.

In some implementations, each of the mounting surfaces of the bulk compressor forms a collar surrounding a light passage, and each of the optical components of the bulk compressor is disposed for use in reflection and has a front face comprising a peripheral portion mounted in direct contact with the collar formed by the respective one of the mounting surfaces. The optical components may be glued to the mounting block from the side.

In accordance with another aspect, there is provided a stretcher-compressor pair for use with an amplifier in a chirped pulse amplification system. The stretcher-compressor pair comprises:a pulse stretcher having an input port configured to receive input optical pulses and an output port configured to output stretched optical pulses, the pulse stretcher comprising an optical fiber provided with a fiber Bragg grating (FBG) having a dispersion profile designed to stretch the input optical pulses, said pulse stretcher further comprising and a tuning mechanism coupled to the FBG for tuning said dispersion profile; anda bulk compressor having an input configured to receive amplified stretched optical pulses and an output configured to output amplified compressed optical pulses, the bulk compressor comprising a mounting block made of solid material and defining a plurality of mounting surfaces, the bulk compressor further comprising a plurality of optical components mounted on the mounting block in a fixed mutual spatial relationship, each of the optical components being rigidly affixed to a respective one of the mounting surfaces.

In some implementations, the pulse stretcher comprises a circulator successively connecting said input port, an FBG port connected to said optical fiber to direct the input optical pulses towards the FBG and receiving the stretched optical pulses and said output port.

In some implementations, the FBG has a grating period with a pre-existing chirp and the tuning mechanism is configured to modify said chirp. In other variants, the FBG has a uniform grating period and the tuning mechanism is configured to impose a chirp thereon.

In some implementations, the tuning mechanism is configured to apply a temperature variation to the optical fiber which is non-uniform along the FBG and may comprises an elongated heat conductive member in thermal contact with the optical fiber provided along said FBG, and a plurality of heat pumping elements in contact with the elongated heat conductive member and distributed along a length thereof.

In some implementations, the tuning mechanism is configured to apply a strain on the optical fiber which is non-uniform along the FBG.

In some implementations, the mounting block of the bulk compressor is a monolithic structure and may be made of a machinable and thermally stable material.

In some implementations, each optical component of the bulk compressor is one of a grating, a lens, or a mirror.

In some implementations, the optical components of the bulk compressor are mounted into a Treacy configuration.

In some implementations, the bulk compressor comprises an input receiving the amplified stretched optical pulses as an input beam, and the optical components of the bulk compressor comprise a first grating angularly dispersing the input beam,

a second grating spatially dispersing the input beam and a pair of plane mirrors shifting and retro-reflecting the input beam for retro-propagation through the second grating and first grating. The pair of plan mirrors may be disposed in a rooftop configuration.

In some implementations, at least one or each of the mounting surfaces of the bulk compressor forms a collar surrounding a light passage, and the optical component affixed to said mounting surfaces has a front face comprising a peripheral portion mounted in direct contact with said collar. The optical components may be glued to the mounting block from the side.

In accordance with another aspect, there is provided a bulk compressor for use with an amplifier in a chirped pulse amplification system comprising a tunable pulse stretcher. The bulk compressor comprises a mounting block formed as a monolithic structure and having an input configured to receive stretched optical pulses and an output configured to output compressed optical pulses. The mounting block is made of solid material and defines a plurality of mounting surfaces each forming a collar surrounding a light passage. The bulk compressor further includes a plurality of optical components mounted on the mounting block in a fixed mutual spatial relationship. Each of the optical components has a front face comprising a peripheral portion mounted in direct contact with the collar formed by a respective one of the mounting surfaces.

In some implementations, the mounting block is made of a machinable and thermally stable material.

In some implementations, each optical component is one of a grating, a lens, or a mirror.

In some implementations, the optical components are mounted into a Treacy configuration.

In some implementations, the optical components comprise a first grating angularly dispersing the stretched optical pulses, a second grating spatially dispersing the stretched optical pulses, and a pair of plane mirrors shifting and retro-reflecting the stretched optical pulses for retro-propagation through the second grating and first grating. The pair of plan mirrors may be disposed in a rooftop configuration.

In some implementations, the optical components are glued to the mounting block from the side. The mounting block comprises side walls surrounding each of said collars, and further comprise a plurality of side holes extending through said sides walls for receiving an adhesive therethrough.

In accordance with another aspect, there is provided a method of manufacturing a bulk compressor, comprising:a) machining a monolithic mounting block in a solid and thermally stable material, said mounting block defining a plurality of mounting surfaces each forming a collar surrounding a light passage; andb) mounting a plurality of optical components on the mounting block in a fixed mutual spatial relationship, said mounting comprising, for each optical component:i. positioning a front face of the optical component in direct contact with the collar formed by a respective one of the mounting surfaces of the mounting block;ii. providing a temporary fixture to hold said optical component in place;iii. gluing the optical component to the mounting block from the side using an adhesive;iv. once said adhesive has cured, removing the temporary fixture.

In some implementations, each optical component is one of a grating, a lens, or a mirror.

In some implementations, the optical components are mounted into a Treacy configuration.

In some implementations, the bulk compressor comprises an input receiving amplified stretched optical pulses as an input beam, and the optical components of the bulk compressor comprise a first grating angularly dispersing the input beam,

a second grating spatially dispersing the input beam, and a pair of plane mirrors shifting and retro-reflecting the input beam for retro-propagation through the second grating and first grating. The pair of plan mirrors may be disposed in a rooftop configuration.

In some implementations, the gluing the optical component to the mounting block from the side comprises inserting said adhesive through side holes provided through side walls surrounding each of said collars.

In some implementations, the temporary fixture comprises a clamp.

In some implementations, the method further comprises a step adjusting a clocking angle of at least one of said optical components.

In accordance with yet another aspect, there is provided a method for amplifying input optical pulses, comprising, successively:a) stretching the input optical pulses into stretched optical pulses using a Fiber Bragg grating (FBG) having a tunable dispersion profile;b) amplifying the stretched optical pulses into amplified stretched optical pulses; andc) compressing the amplified stretched optical pulses into amplified compressed optical pulses using a bulk compressor comprising a mounting block made of solid material and defining a plurality of mounting surfaces, the bulk compressor further comprising a plurality of optical components performing said compressing and mounted on the mounting block in a fixed mutual spatial relationship, each of the optical components being rigidly affixed to a respective one of the mounting surfaces; andd) providing a feedback loop measuring and analysing the amplified compressed optical pulses and tuning the dispersion profile of the FBG in view of said analysing.

In some implementations, the stretching of the optical pulses comprises providing a circulator successively connecting an input port for receiving the input optical pulses, an FBG port connected to an optical fiber hosting said FBG to direct the input optical pulses towards the FBG and receiving the stretched optical pulses, and an output port for directing the stretched optical pulses towards the amplifier.

In some implementations, the FBG has a chirped grating period.

In some implementations, the tuning of the dispersion profile of the FBG comprises applying a temperature variation which is non-uniform along the FBG.

In some implementations, the tuning of the dispersion profile of the FBG comprises applying a strain to an optical fiber hosting the FBG which is non-uniform along the FBG.

In some implementations, the feedback loop comprises adjusting the dispersion profile of the FBG of the pulse stretcher to compensate for misalignments of the bulk compressor.

In some implementations, the feedback loop comprises adjusting the dispersion profile of the FBG of the pulse stretcher to compensate for manufacturing errors of said bulk compressor.

In some implementations, the feedback loop comprises adjusting the dispersion profile of the FBG of the pulse stretcher to compensate for nonlinear effects induced in the amplified stretched optical pulses.

In some implementations, the amplifying of the stretched optical pulses comprises using a fiber amplifier.

Advantageously, the bulk compressor described herein defines a fixed and sturdy structure, which simplifies its use compared to traditional devices. In a typical tunable bulk grating-based pulse compressor, each optical component is physically disjoint from the other components. This makes the correct placement and alignment of the components a cumbersome and tedious process. By contrast, the CPA system described herein relies on the tunability of the pulse stretcher for adjustments, combined with a compressor having fixed grating parameters and free of moving parts. This simplifies the usual grating pair alignment process greatly, since this alignment is essentially dictated by the mounting block. The alignment complexity issues are therefore transferred to machining tolerance issues, which are much easier to manage.

In accordance with another aspect, there is provided a stretcher-compressor pair for use with an amplifier in a chirped pulse amplification system. The stretcher-compressor pair includes a pulse stretcher having an input configured to receive input optical pulses and an output configured to output stretched optical pulses. The pulse stretcher includes a fiber Bragg grating (FBG) having a dispersion profile designed to stretch optical pulses, and a tuning mechanism coupled to the FBG for tuning said dispersion profile.

The stretcher-compressor pair further includes a bulk compressor having an input configured to receive amplified stretched optical pulses and an output configured to output amplified compressed optical pulses. The bulk compressor includes a mounting block made of solid material and defining a plurality of mounting surfaces, the bulk compressor further comprising a plurality of optical components mounted on the mounting block in a fixed mutual spatial relationship, each of the optical components being rigidly affixed to a respective one of the mounting surfaces.

In other implementations, there may also be provided a bulk compressor as described above provided for use in a CPA system in conjunction with an amplifier and a pulse stretcher having an FBG and a tuning mechanism coupled to said FBG.

Other features and advantages will be better understood upon reading of embodiments thereof with reference to the appended drawings.

