Frequency comb has shown remarkable potential in time/frequency metrology, atomic/molecular spectroscopy and precision LIDARs. It will create novel possibilities in nano-photonics and plasmonics; however, its interrelation with surface plasmons is unexplored despite the important role that plasmonics play in nonlinear spectroscopy and quantum optics through the manipulation of light in a subwavelength scale. We demonstrate that frequency comb can be transferred by plasmonic nanostructures without noticeable degradation of less than 6.51×10-19 in absolute position and 1 Hz in linewidth, which implies frequency comb’s potential applications in nanoplasmonic spectroscopy, quantum metrology and subwavelength photonic circuits.
Recently, Fiber Bragg Grating (FBG) sensors are being used for motion tracking applications. However, the sensitivity, linearity and stability of the systems have not been fully studied. Herein, an embroidered optical Fiber Bragg Grating (FBG) on a stretchable supportive textile for elbow movement measurement was developed. The sensing principle of this system is based on the alteration of Bragg wavelength due to strain from the elbow movements. The relationship between elbow movements and reflected Bragg wavelength was found to be linear. The dynamic range of FBG sensor on elbow support is between 0 and 120 degree. Finally, the stability of the FBG sensor on the supportive textile was tested during the exercise and the cleaning process with water. The sensitivity of FBG sensors for joint angle measurement and the effect of the movement and cleaning process to signals from FBG sensors after using in the real activity will be the basis knowledge for design and actual implementation of future optical fiber based wearable devices.
We report a novel stabilization method for two frequency combs with a small relative fceo jitter using a selected single optical mode out of a frequency comb. This proposed method is intended to stabilize optical frequencies which generated by two different optical combs with immunity to environmental disturbance, frequency drift and fluctuation with time so as to enhance the measuring performance of dual comb based spectroscopy and distance measurement. A single comb mode is selected out using a composite optical filtering and diode laser injection locking. The selected optical frequency yields a narrow relative linewidth less than 1 Hz and the frequency stability of 1.58×10-17 at 10 s averaging time. By using this, we generated heterodyned beat signal between generated optical frequency and another comb to stabilize relative fceo using phase lock-in control which adjust driving frequency of acousto-optic modulator. As a result of feedback control, the relative jitter is well stabilized down to 1.06×10-15 at 10 s averaging time. This highly stable frequency instability of two combs can perform to enhance the measuring resolution, accuracy and repeatability for dual comb based spectroscopy and distance metrology.
Generating multiple optical frequencies referenced to the frequency standard is an important task in optical clock dissemination and optical communication. An apparatus for frequency-comb-referenced generation of multiple optical frequencies is demonstrated for high-precision free-space transfer of multiple optical frequencies. The relative linewidth and frequency instability at each channel corresponds to sub-1 Hz and 1.06×10-15 at 10 s averaging time, respectively. During the free-space transfer, the refractive index change of transmission media caused by atmospheric turbulences induces phase and frequency noise on optical frequencies. These phase and frequency noise causes induced linewidth broadening and frequency shift in optical frequencies which can disturb the accurate frequency transfer. The proposed feedback loop with acousto-optic modulator can monitor and compensate phase/frequency noise on optical frequencies. As a result, a frequency-comb-referenced single optical mode is compensated with a high signal to noise ratio (SNR) of 80 dB. By sharing the same optical paths, this feedback loop is confirmed to be successfully transferred to the neighboring wavelength channels (a 100 GHz spaced channel). This result confirms our proposed system can transfer optical frequencies to the remote site in free-space without performance degradation.
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