6 Direct Femtosecond Laser Writing of Optical Waveguides …
201
of solid-state waveguide systems for broadband lasing covering wavelength from
visible till mid-infrared have been realized.
Visible waveguide lasing at red light wavelength band-based Pr-doped crystals
waveguides reaches the output powers of tens of mW [53, 94, 95]. In the near infrared
regime, the Ti:sapphire waveguide lasing from 700 to 870 nm was realized, with the
maximum output power of 143 mW at 800 nm, and a slope efficiency of 23.5% [98].
Based on laser-written waveguides of Yb:YAG crystal, the recent work has shown
the maximum output power to be ~5 W or even higher with the optimization of the
optical pump system of waveguide lasers [123]. The slope efficiency of waveguide
lasing at 1 µm also reaches high values close to the quantum limit. The reported
results on 1.8–2 µm lasing band have been realized in Tm:YAG and Tm:KLuW
cladding waveguides, and maximum output power of 93 and 46 mW was achieved,
respectively [106, 111]. For typical mid-infrared wavelength regime, by using laserwritten waveguides in Cr or Fe-doped ZnSe or ZnS, lasing from 2.5 µm has been
realized with maximum output power of 5.1 W [107].
In addition to the continuous-wave waveguide lasing, people have developed Qswitched and mode-locked systems to achieve pulsed waveguide lasers, by using
saturable absorbers (such as SESAMs, graphene, MoS 2 , carbon nanotubes) [11].
The obtained repetition rate of the Q-switched waveguide lasers reaches MHz, and
the maximum output power can be as high as a few watts [124]. The lasing at 2 µm
with Q-switched mode-locking based on graphene reaches 7.8 GHz from a Tm:YAG
ceramic waveguide [125]. Figure 6.9 shows typical pulsed lasing performance from
a laser-written Nd:YVO 4 waveguide based on graphene Q-switching [126].
Another advantage of waveguide lasers over bulk systems is that lasing with
tailored beam output can be realized in waveguides. By applying direct optical pump
into the 3D waveguide in gain media, lasing generation at 1 µm with beam splitting
(e.g., 1 × 2, 1 × 3, and 1 × 4) or ring-shaped transformation has been achieved in
laser-written Nd or Yb-doped YAG waveguides [61, 121]. In addition, optical-latticelike cladding structures based on Nd:YAP crystal is an ideal platform to get lattice-like
lasing [117]. The powerful 3D microprocessing ability of direct femtosecond laser
writing may offer more intriguing devices for lasing as miniature light sources.
Waveguide amplifiers are key devices in telecommunication systems. The amplification at C-band (centered at 1.55 µm) is of special importance to industries,
and Er-doped glass waveguides are typically used as amplifiers, which are called
“EDWA” (erbium-doped waveguide amplifier) in the communication systems. Direct
femtosecond laser writing has been utilized to manufacture channel waveguides in
a few glass families, including Er-doped or Er, Yb-codoped phosphates, oxyfluoride
silicates, phospho-tellurites, bismuthates, and chalcogenides, to realize amplification at telecommunication bands [15]. Figure 6.10 shows the fiber-to-fiber net gain
spectra under different pump powers in an Er-doped bismuthate glass waveguide for
C-band. As pumped of 1050 mW at 980 nm, the amplifier exhibits a peak internal
gain per unit length of 2.3 dB/cm at 1533 nm and a peak fiber-to-fiber net gain of
16.0 dB at 1533 nm [127].
201
of solid-state waveguide systems for broadband lasing covering wavelength from
visible till mid-infrared have been realized.
Visible waveguide lasing at red light wavelength band-based Pr-doped crystals
waveguides reaches the output powers of tens of mW [53, 94, 95]. In the near infrared
regime, the Ti:sapphire waveguide lasing from 700 to 870 nm was realized, with the
maximum output power of 143 mW at 800 nm, and a slope efficiency of 23.5% [98].
Based on laser-written waveguides of Yb:YAG crystal, the recent work has shown
the maximum output power to be ~5 W or even higher with the optimization of the
optical pump system of waveguide lasers [123]. The slope efficiency of waveguide
lasing at 1 µm also reaches high values close to the quantum limit. The reported
results on 1.8–2 µm lasing band have been realized in Tm:YAG and Tm:KLuW
cladding waveguides, and maximum output power of 93 and 46 mW was achieved,
respectively [106, 111]. For typical mid-infrared wavelength regime, by using laserwritten waveguides in Cr or Fe-doped ZnSe or ZnS, lasing from 2.5 µm has been
realized with maximum output power of 5.1 W [107].
In addition to the continuous-wave waveguide lasing, people have developed Qswitched and mode-locked systems to achieve pulsed waveguide lasers, by using
saturable absorbers (such as SESAMs, graphene, MoS 2 , carbon nanotubes) [11].
The obtained repetition rate of the Q-switched waveguide lasers reaches MHz, and
the maximum output power can be as high as a few watts [124]. The lasing at 2 µm
with Q-switched mode-locking based on graphene reaches 7.8 GHz from a Tm:YAG
ceramic waveguide [125]. Figure 6.9 shows typical pulsed lasing performance from
a laser-written Nd:YVO 4 waveguide based on graphene Q-switching [126].
Another advantage of waveguide lasers over bulk systems is that lasing with
tailored beam output can be realized in waveguides. By applying direct optical pump
into the 3D waveguide in gain media, lasing generation at 1 µm with beam splitting
(e.g., 1 × 2, 1 × 3, and 1 × 4) or ring-shaped transformation has been achieved in
laser-written Nd or Yb-doped YAG waveguides [61, 121]. In addition, optical-latticelike cladding structures based on Nd:YAP crystal is an ideal platform to get lattice-like
lasing [117]. The powerful 3D microprocessing ability of direct femtosecond laser
writing may offer more intriguing devices for lasing as miniature light sources.
Waveguide amplifiers are key devices in telecommunication systems. The amplification at C-band (centered at 1.55 µm) is of special importance to industries,
and Er-doped glass waveguides are typically used as amplifiers, which are called
“EDWA” (erbium-doped waveguide amplifier) in the communication systems. Direct
femtosecond laser writing has been utilized to manufacture channel waveguides in
a few glass families, including Er-doped or Er, Yb-codoped phosphates, oxyfluoride
silicates, phospho-tellurites, bismuthates, and chalcogenides, to realize amplification at telecommunication bands [15]. Figure 6.10 shows the fiber-to-fiber net gain
spectra under different pump powers in an Er-doped bismuthate glass waveguide for
C-band. As pumped of 1050 mW at 980 nm, the amplifier exhibits a peak internal
gain per unit length of 2.3 dB/cm at 1533 nm and a peak fiber-to-fiber net gain of
16.0 dB at 1533 nm [127].