the light emission from the laser to the photodetector. The useful volume of the
single optical fiber in OEO with RF FODL is less than 1 cm
3 per 1 km of the fiberoptical thread with the total delay in RF FODL of 5 μs/km. For instance, for the
single-mode optical fiber with 1 km-length and the thread diameter of 7–10 μm, the
quarts envelope of 21 μm, the total diameter of 33 μm, the useful volume is about
1 cm
3 . In the limit case, we have for the single-mode optical fiber with 1 km-length
with the thread diameter of 2 μm, with the quartz envelope diameter 9 μm, the total
optical fiber diameter of 11 μm, the useful volume is about 0.1 cm
3 with the total
delay in RF FODL of 5 μm/km with transmission via RF FODL of microwave
oscillations with the frequency of 10 GHz.
At development of the ultrasmall in the volume of RF FODL of 1 cm
3 and less,
the main technological problem is the increasing optical losses, which are formed at
splicing owing to the small radii of the optical fiber bending during splicing. So, for
optical fiber thread packing at 1 km-length, approximately 10,000–50,000 turns are
required at the average turn length of 18–30 mm with the bending radii about
3–5 mm.
The rough calculation at the bending radius of 10 mm, at losses of 0.0002 dB/
1bend at number of such bends of 10,000 pieces allows obtaining the losses value on
2 dB-level per 1 km of the optical fiber, which satisfies to the practical application of
RF FODL.
At manufacture of the ultrasmall RF FODL in volume, the rolling process is
specially important for the lengthy thread of the optical fibers produced with old
traditional technologies of the vapor-phase deposition with utilization of the plasma
torches at small curvature radii less than 15 mm. Figure 2.13d, e shows the plot of the
optical loss function of the traditional optical fibers and the photo-crystal
(or perforated) fibers versus the value of the bending radius for different fibers [22].
The transverse sections of the fiber with the one-dimension circular structure (the
Braggian fiber) (d) and the photon-crystal fiber with auxiliary holes around the
thread (e) are presented in Fig. 2.13d, e together with the example of the transmission
function versus the wavelength in the Braggian fiber.
At present, in Russia and in many countries, the whole series of new types of
optical fibers exists, which allow the bend practically under any angles and at that,
have the insignificant losses in the bending. These are so-called photon-crystal fibers
(PCF) having in addition the whole series of other remarkable properties.
Modern technologies of the quartz optical fiber manufacture with the nitrogen
doping with manufacture of the variety of high-accuracy envelopes give a possibility
to produce of optical fibers with low losses at limit bending radii less than 5 mm. In
perspective, at utilization of patented by authors high-accuracy technology of optical
fiber manufacture with application of the half-finished product heating with the help
of the plasma pillar created by the microwave oscillators, we can produce the optical
fibers with ultralow optical losses at small bending radii less than 5 mm. This
patented technology and the small useful volume of the optical fiber in OEO with
RF FODL give us the right to state that the limit volume of RF FODL with the single
lengthy optical fiber is 0.1 cm
3 /1 km of the optical fiber at delay 5 μs/km.
7.5 Parametric Frequency Instability of OEO with RF FODL at Temperature Impact of. . . 431
single optical fiber in OEO with RF FODL is less than 1 cm
3 per 1 km of the fiberoptical thread with the total delay in RF FODL of 5 μs/km. For instance, for the
single-mode optical fiber with 1 km-length and the thread diameter of 7–10 μm, the
quarts envelope of 21 μm, the total diameter of 33 μm, the useful volume is about
1 cm
3 . In the limit case, we have for the single-mode optical fiber with 1 km-length
with the thread diameter of 2 μm, with the quartz envelope diameter 9 μm, the total
optical fiber diameter of 11 μm, the useful volume is about 0.1 cm
3 with the total
delay in RF FODL of 5 μm/km with transmission via RF FODL of microwave
oscillations with the frequency of 10 GHz.
At development of the ultrasmall in the volume of RF FODL of 1 cm
3 and less,
the main technological problem is the increasing optical losses, which are formed at
splicing owing to the small radii of the optical fiber bending during splicing. So, for
optical fiber thread packing at 1 km-length, approximately 10,000–50,000 turns are
required at the average turn length of 18–30 mm with the bending radii about
3–5 mm.
The rough calculation at the bending radius of 10 mm, at losses of 0.0002 dB/
1bend at number of such bends of 10,000 pieces allows obtaining the losses value on
2 dB-level per 1 km of the optical fiber, which satisfies to the practical application of
RF FODL.
At manufacture of the ultrasmall RF FODL in volume, the rolling process is
specially important for the lengthy thread of the optical fibers produced with old
traditional technologies of the vapor-phase deposition with utilization of the plasma
torches at small curvature radii less than 15 mm. Figure 2.13d, e shows the plot of the
optical loss function of the traditional optical fibers and the photo-crystal
(or perforated) fibers versus the value of the bending radius for different fibers [22].
The transverse sections of the fiber with the one-dimension circular structure (the
Braggian fiber) (d) and the photon-crystal fiber with auxiliary holes around the
thread (e) are presented in Fig. 2.13d, e together with the example of the transmission
function versus the wavelength in the Braggian fiber.
At present, in Russia and in many countries, the whole series of new types of
optical fibers exists, which allow the bend practically under any angles and at that,
have the insignificant losses in the bending. These are so-called photon-crystal fibers
(PCF) having in addition the whole series of other remarkable properties.
Modern technologies of the quartz optical fiber manufacture with the nitrogen
doping with manufacture of the variety of high-accuracy envelopes give a possibility
to produce of optical fibers with low losses at limit bending radii less than 5 mm. In
perspective, at utilization of patented by authors high-accuracy technology of optical
fiber manufacture with application of the half-finished product heating with the help
of the plasma pillar created by the microwave oscillators, we can produce the optical
fibers with ultralow optical losses at small bending radii less than 5 mm. This
patented technology and the small useful volume of the optical fiber in OEO with
RF FODL give us the right to state that the limit volume of RF FODL with the single
lengthy optical fiber is 0.1 cm
3 /1 km of the optical fiber at delay 5 μs/km.
7.5 Parametric Frequency Instability of OEO with RF FODL at Temperature Impact of. . . 431