# US 8,570,646 B2 · Modular, high energy, widely-tunable ultrafast fiber source

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- Number: US 8,570,646 B2
- Document ID: US8570646B2
- Status: Granted
- Kind: B2
- Application number: 13/187,566
- Filed: 2011-07-21
- Published: 2011-11-17
- Granted: 2013-10-29
- Earliest claimed: 2000-05-23
- Assignees: Imra America, Inc.
- Applicants: Martin E. Fermann
- Inventors: Martin E. Fermann
- Web page: https://patentgrep.com/patent/US8570646B2

## CPC

- H01S 3/1115: using intracavity saturable absorbers
- H01S 3/06754: {Fibre amplifiers (H01S3/06708 takes precedence)}
- H01S 3/1112: Passive mode locking
- H01S 3/302: {in an optical fibre}
- H01S 3/0057: {Temporal shaping, e.g. pulse compression, frequency chirping (soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108)}
- H01S 3/0675: {Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers}
- H01S 3/094019: {Side pumped fibre, whereby pump light is coupled laterally into the fibre via an optical component like a prism, or a grating, or via V-groove coupling}
- H01S 3/094042: {of a fibre laser}
- H01S 3/109: Frequency multiplication, e.g. harmonic generation
- H01S 3/1616: {thulium}
- H01S 3/1618: {ytterbium}
- 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

## Abstract

A modular, compact and widely tunable laser system for the efficient generation of high peak and high average power ultrashort pulses. Modularity is ensured by the implementation of interchangeable amplifier components. System compactness is ensured by employing efficient fiber amplifiers, directly or indirectly pumped by diode lasers. Peak power handling capability of the fiber amplifiers is expanded by using optimized pulse shapes, as well as dispersively broadened pulses. Dispersive broadening is introduced by dispersive pulse stretching in the presence of self-phase modulation and gain, resulting in the formation of high-power parabolic pulses. In addition, dispersive broadening is also introduced by simple fiber delay lines or chirped fiber gratings, resulting in a further increase of the energy handling ability of the fiber amplifiers. The phase of the pulses in the dispersive delay line is controlled to quartic order by the use of fibers with varying amounts of waveguide dispersion or by controlling the chirp of the fiber gratings. After amplification, the dispersively stretched pulses can be re-compressed to nearly their bandwidth limit by the implementation of another set of dispersive delay lines. To ensure a wide tunability of the whole system, Raman-shifting of the compact sources of ultrashort pulses in conjunction with frequency-conversion in nonlinear optical crystals can be implemented, or an Anti-Stokes fiber in conjunction with fiber amplifiers and Raman-shifters are used.

## Claims

### Claim 1

A laser system producing pulses in the 3-5 μm wavelength region, comprising:
a pulse source comprising a passively mode locked fiber oscillator, said pulse source configured to produce pulses at wavelengths in the 1.5-2.2 μm wavelength region and in a gain spectrum of a Tm or Ho fiber amplifier; and
a first frequency shifting optical fiber disposed downstream from said pulse source and having an infrared absorption edge longer than that of silica, said first frequency shifting fiber configured to frequency shift said pulses to said 3-5 μm wavelength region.

### Claim 2 (depends on 1)

A laser system according to claim 1, wherein said pulse source comprises:
a second fiber frequency shifter inputting pulses from said mode locked fiber oscillator and producing said pulses in said 1.5-2.2 wavelength region.

### Claim 3 (depends on 2)

A laser system according to claim 2, wherein said second frequency shifting optical fiber comprises polarization maintaining fiber.

### Claim 4 (depends on 2)

A laser system according to claim 2, wherein said second frequency shifting optical fiber is tapered along the fiber length to reduce the core size for dispersion control.

### Claim 5 (depends on 2)

A laser system according to claim 2, wherein said second frequency shifting optical fiber comprises holey optical fiber.

### Claim 6 (depends on 2)

A laser system according to claim 2, wherein said second frequency shifting optical fiber comprises silica optical fiber.

### Claim 7 (depends on 2)

A laser system according to claim 2, further comprising a plurality of fiber amplifiers alternately connected between said first and said second fiber frequency shifters.

### Claim 8 (depends on 1)

A laser system according to claim 1, wherein said pulse source comprises an Er mode locked fiber oscillator.

### Claim 9 (depends on 1)

A laser system according to claim 1, wherein said first frequency shifting optical fiber comprises fluoride- based Raman-shifting optical fiber.

### Claim 10 (depends on 1)

A laser system according to claim 1, wherein said mode locked fiber oscillator generates nearly bandwidth limited femtosecond pulses.

### Claim 11 (depends on 1)

A laser system according to claim 1, wherein said pulses in said 1.5-2.2 μm wavelength region comprise femtosecond pulse widths.

### Claim 12 (depends on 1)

A laser system according to claim 1, wherein said pulse source comprises a Tm or Ho fiber laser.

### Claim 13 (depends on 1)

A laser system according to claim 1, further comprising a Tm or Ho fiber amplifier disposed downstream from said pulse source.

### Claim 14 (depends on 1)

A laser system according to claim 1, wherein said laser system is arranged in a system for spectroscopy.