Supercontinuum Generation by Nonlinear Optics - Optical Signal Processing by Silicon Photonics - page 75

0.3 mW/nm for peak power of input radiation achieved within the spectral range of
530-1,100 nm. Such sources with peak powers at nanometer can be used for
nanoscale systems [ 27 ]. 100 fs pulses at 1,560 nm were launched into sub-5 cm
section of highly nonlinear fiber exhibit spectral broadening over 700 nm and third
harmonic radiation over 520 nm [ 28 ]. 250 fs pulses from Yb:KYW laser with the
average power of 150 mW centered at the wavelength of 1,046 nm has been supplied
to amplifier input. In this spectral broadening with spectrum width of 50 nm and with
average spectral power density of higher than 65 mW/nm is achieved [ 29 ].
6.8 Applications of SC Generation
SC sources are the substitute of white light, tungsten-based sources which are used
in characterization of broadband attenuation, spectroscopy, and microscopy setups.
The major drawback of white light sources is the low brightness that is finding
out by the filament temperature. Larger filaments with same brightness are used in
sources with high power at output; therefore same power can be coupled to single
mode fiber.
There is also an issue of coupling of all incandescent light sources to fiber. The
light coupling efficiency is very low that results in small fraction of light will be
available into fiber. The SC sources resolve both the issues of coupling and inten-
sity and give the possibility of making sources that has spectral width like white
light sources and intensity of a laser.
There is big problem of pump source in replacement sources of white light with
the SC. An incandescent light or white light sources are cost-effective (can be con-
struct from few of hundred dollars) and takes very small space of laboratory. On
the other hand, SC sources needs large pump source (a large femtosecond laser
system) and this would not build up more compact and cost-effective SC sources.
This problem can be resolved by increasing the bandwidth of spectral broadening
and reducing power at threshold [ 16 ]. This is achieved by using sources of pico-
seconds or nanosecond pulses centered at 1,060 nm wavelength that leads to less
cost, portable, and compact devices [ 19 ].
Most SC experiments yield output in the mW-range, but systems with high
average power have also been realized. For example, a 900 nm broad SC source
with an average output power of 2.4 W was recently demonstrated [ 20 ]. The out-
put was generated by pumping a 1 m long PCF with zero dispersion wavelengths
at 975 nm. The fiber was pumped by a mode-locked Nd: YVO4 laser with a pulse
length of 10 ps, repetition rate of 85 MHz, and an average power of 5 W. The
complete system is simple and compact (500 × 250 × 100 mm 3 ) and potentially
cost-effective.
Therefore, poor resolution is caused by long wavelengths because of the rea-
son that the spectral width of the source is not large satisfactorily. Sources for
OCT typically are sources based on amplified spontaneous-emission, super
luminescent diodes, and ASE, from semiconductors or doped fibers. For all these