curve in Fig.7.28. Thereby highly sensitive physical, chemical, and biological
sensing functions can be enabled with a compact device.
7.10 Summary
Numerous embodiments of opticalfibers and optical waveguide structures using
different materials and configurations have been investigated to form optical probes,
molecular and disease analysis tools, health monitoring devices, and biosensors.
A wide variety of biosensors are available to selectively detect specific biological
elements, such as microorganisms, organelles, tissue samples, cells, enzymes,
antibodies, and nucleic acids derived from animal tissue and bodyfluids, human
tissue and bodyfluids, cell cultures, foods, or air, water, soil, and vegetation
samples. In addition to analyzing biological elements, diverse types of
photonics-based biosensors are being used in the healthcarefield for assessments of
dental conditions and materials, in equipment for biomechanics and rehabilitation
applications, in the diagnosis of gastrointestinal disorders, and in smart textiles for
respiratory monitoring. Supporting optical and photonics technologies includefiber
Bragg gratings, opticalfilters, interferometry methodologies, nanoparticle arrays,
and surface plasmon resonance techniques.
7.11 Problems.
7 :1 Consider the probe configuration shown in Fig.7.3a. Suppose that the
dichroicfilter has the following characteristics: a loss of 1 dB at each cou-
pling junction, reflection loss of 1.7 dB at a wavelengthλ 1 , and a trans-
mission loss of 1.7 dB at a wavelengthλ 2. (a) If the optical source launches
10 mW of power into thefirst coupling junction of the dichroicfilter, show
that the optical power level at the tissue surface is 6.9 dBm (4.9 mW). (b) If
the opticalfiber probe at the tissue surface collects a power level of 10μWat
a wavelength λ 2 , show that the power level at the photodetector is
−23.1 dBm (4.9μW).
7 :2 Consider the probe configuration shown in Fig.7.3b. Suppose that the
optical circulator has the following characteristics: a loss of 1 dB at each
coupling junction and an insertion loss of 1.7 dB at both wavelengthλ 1 and
wavelengthλ 2. (a) If the optical source launches 10 mW of power into the
first coupling junction of the circulator, show that the optical power level at
the tissue surface is 6.3 dBm (4.3 mW). (b) If the opticalfiber probe at the
tissue surface collects a power level of 10μW at a wavelengthλ 2 , show that
the power level at the photodetector is−23.7 dBm (4.3μW).
7 :3 Consider the experimental setup shown in Fig.7.5. Suppose the internal
intrinsic loss plus the power splitting loss of the coupler add up to 3.7 dB and7.9 Optical Fiber Nanoprobes 227