Hermann Lin

Waveband-tunable multiwavelength erbium-doped fiber laser

A waveband-tunable multiwavelength erbium-doped fiber laser based on a novel integrated structure of nonlinear polarization rotation and an unbalanced in-line Sagnac interferometer is proposed and demonstrated. An ultrabroadband lasing spectrum with 140 wavelength lasing peaks periodically distributed from 1563 to 1612.5 nm accompanied by a lasing linewidth of 0.112 nm, a free spectral range (FSR) of 0.32 nm, and a signal-to-noise ratio (SNR) of 20 dB has been achieved. A laser with high-wavelength lasing and waveband tunability was also achieved by merely adjusting the polarization controllers. The wavebands can be tuned from 1567 to 1606 nm continuously. Thirty-one lasing wavelengths in a 3 dB flattened spectrum has been achieved with a SNR of 48 dB, a linewidth of 0.03 nm, and a FSR of 0.32 nm. Good stability of the laser operating at room temperature has been verified by using an optical spectrum analyzer to measure every 2 min for a half-hour.

High power C+L-band Erbium ASE source using optical circulator with double-pass and bidirectional pumping configuration.

We have proposed and demonstrated a high-power C+L-band erbium amplified spontaneous emission source using an optical circulator with double-pass and bi-directional configuration, which can provide a high output power of 177.8 mW with a ripple of 5 dB and a wide line width of 81.0 nm (1525.1-1606.1 nm) without adding any external spectra-flattening components. This designed configuration is also considered relaxing resonant lasing for averaged power stability with +/- 0.013 dB, allowing high pumping efficiency of 32.8%.

Multi-wavelength-switchable and Uniform Erbium-doped Fiber Laser Using Unbalanced In-line Sagnac Interferometer.

We have proposed and demonstrated a multi-wavelength-switchable and uniform erbium-doped fiber laser using unbalanced in-line Sagnac Interferometer. By employing this simple scheme and through the proper control of the polarization controller, we were able to achieve uniform multi-wavelength operation of up to 84 laser lines with the signal-to- noise ratio over 20dB and 0.8-nm wavelength switching at room temperature. Again, we generated more than 300 lines, 0.1-m wavelength switching and good power stability (</= 0.2dB) over 1570nm-1610nm in the experiment.

Modified phase-generated carrier demodulation compensated for the propagation delay of the fiber.

In general applications, the output signals of the fiber-optic interferometric sensor (FOIS) need some demodulation techniques to linearly demodulate the sensing phase signal. The common signal demodulation circuit of the FOIS is passive homodyne demodulation using phase-generated carrier [(PGC) demodulation]. Preliminary analysis of the research demonstrates that a variation in the output demodulated signal is related to the length of the fiber, and the output demodulated signal will approach zero at some certain lengths of the fiber. To improve the performance of the FOIS, it is necessary to develop the modified PGC demodulation to compensate for the propagation delay of the fiber.

Modified in-line Sagnac interferometer with passive demodulation technique for environmental immunity of a fiber-optic current sensor

A modified in-line Sagnac interferometer (MISI) with passive demodulation Technique (PDT) was proposed to immunize the fiber-optic current sensor (FOCS) from environmental perturbations. A large vibration to simulate the environmental perturbations with acceleration up to 12 g was applied to the lead fiber of the FOCS. The noise floor could be significantly suppressed (20 dB) by the MISI better than by a conventional interferometer. In the same dynamic environments, the PDT could make the FOCS achieve a good linear demodulation with average distortion rates always lower than 0.9%. In addition, all the sensitivities measured in both static and dynamic environments are all approximately 4.5 microrad/(A(rms) turns), which is close to the literatural data measured in static environments. These considerable achievements of high sensitivity, environmental immunity, and free electric shock concerns may lead FOCSs to field-monitoring applications of power delivery lines.

Erbium-Doped Fiber-Ring-Laser-Based Supercontinnum Source Using Nonlinear Polarization-Rotation and Stimulated Raman Scattering

We have demonstrated a simple supercontinnum source based on an erbium-doped fiber-ring laser incorporating both schemes of nonlinear polarization rotation and stimulated Raman scattering (SRS). The proposed source obtains the spectral width of 165 nm covering from 1523 to 1688 nm accompanied with a flattened spectrum-ripple less than 3 dB. The small threshold pumping power around 50 mW could effectively activate the SRS so as to significantly expand the spectra for longer wavelength approaching. The relative intensity noise of the laser could be as low as -134 dBc[1 Hz] at the band larger than 5 GHz without harmonics caused by the fiber ring.

Vibration insensitive optical fiber current sensor with a modified reciprocal reflection interferometer

A modified reciprocal reflection interferometer (MRRI) is proposed for vibration insensitive optical fiber current sensors (OFCSs). The verifications of experiments are in good agreement with our theoretical analyses. A large vibrational perturbation applied to a segment of lead fiber to simulate the disturbance to the OFCS can be suppressed over 20 dB compared with a conventional reciprocal reflection interferometer (RRI). The noise floor of the OFCS with an MRRI under perturbations is about 1.36 Armsturns/Hz1/2 near the shot noise limit. A good linear demodulation result is obtained and the evaluation of the Verdet constant 1.1?rad/Arms turns approximates the literatural data measured in static environment.

Fiber-Optic Current Sensor Using Passive Demodulation Interferometric Scheme

An interferometer using a Faraday rotator with 22.5 rotation bias is proposed for the use of a fiber-optic current sensor (FOCS) to demodulate phase signals passively. High sensitivities and extra low distortions are obtained by this passive demodulation interferometric scheme (PDIS). The Verdet constant of optical fibers at 1300 nm is evaluated to be 4.5 murad (A rms.turns), which is in good agreement with the literature. With signal distortions always below 0.8 %, the proposed scheme should be significantly effective for the demodulation needs of an FOCS. The PDIS also could enable a FOCS to directly connect with fiber-optic communication networks for the implementation of long-distance remote and multiplexing sensor systems. Moreover, electric shock concerns on current intensity measurements of high-voltage power delivery systems are greatly reduced.

Method for path imbalance measurement of the two-arm fiber-optic interferometer

The path imbalance (PI) of the two-arm fiber-optic interferometric sensor is a substantial parameter; a precise value of millimeters is required. Currently the precision reflectometry and the millimeter optical time-domain reflectometry are used to measure the tiny optical path difference, but the performances of these measurements are limited from the length and the resolution of the PI. We propose a new method accomplished by interferometer to accurately measure millimeters to within a few decimeters of the PI.

Counting signal processing and counting level normalization techniques of polarization-insensitive fiber-optic Michelson interferometric sensors

A counting signal processing technique of the fiber-optic interferometric sensor is proposed. The technique is capable of counting the numbers of the maximum and minimum of the output interferometric signal in a specific time duration, and it can be used as the basis to distinguish the sensing phase signal. It can also be used as a signal detector on applications such as intrusion detection. All sensors are subject to aging of the optical components and bending loss, and therefore the output signal of each sensor may vary with time. We propose a counting level normalization technique to compensate for these variations and to obtain the correct counting numbers.