George Xiao

A tunable multiwavelength fiber ring laser for measuring polarization-mode dispersion in optical fibers

We describe and demonstrate a tunable triple-wavelength erbium-doped fiber ring laser along with a method of measuring polarization-mode dispersion (PMD) in optical fibers based on a broad-band orthogonal-pump four-wave mixing in a semiconductor optical amplifier. The measured PMD results for optical fibers are in good agreement with values measured by means of commercial PMD testing equipment.

Metallic Environmental Effect on RF-Based Energy Transmission

Radio frequency (RF)-based energy transmission enables controllable and simultaneous power delivery to wireless sensors. In such applications, RF energy transmission is likely to be affected by highly conductive (metallic) environments. Understanding metals influence on power delivery will help improve practical implementation. This letter studies the behavior of RF energy transmission in selected scenarios by measuring return loss and peak received power. Visualized energy flow is simulated to obtain the direct picture of such scenarios. The simulation results are consistent with conclusions drawn from experimental results measured using return loss and peak received power.

High-power multiwavelength Er/sup 3+/-Yb/sup 3+/ codoped double-cladding fiber ring laser

A high-power simultaneous multiwavelength lasing in an Er/sup 3+/-Yb/sup 3+/ codoped double-cladding fiber (EYCDF) ring laser is demonstrated based on a wavelength-dependent filter through spatial mode beating within the multimode fiber section. We have investigated the relationship between the lasing wavelengths and the length of the EYCDFs. The experimental results indicate that both the number of lasing wavelength lines and the spacing between two adjacent lasing lines can be controlled by the changes of the lasing light polarization states.

Optimal position of nonlinear regenerators in optical communication links

We propose a general method of determining the optimal position of nonlinear regenerators and the bit-error-rate (BER) improvement in optical communication links. We calculate the BER improvement as a function of the position of the regenerator and the optical link noise parameter using an ideal regenerator as an example.

Printed single-feed circularly polarized UHF reader antenna for RFID applications

In this paper an optimally designed corner trimmed microstrip UHF reader antenna fabricated using screen printing of silver ink on an FR4 substrate is presented. The reader antenna, 12×12 cm2 in size, is fed through a single microstip line with an SMA connector attached to the antenna board. The measured results demonstrate reflection coefficient better than −15 dB as well as 3dB-beamwidth greater than 60° over the 900 MHz–930 MHz frequency bandwidth. The measured axial ratio lower than 3 dB within the range of 910 MHz–920 MHz shows the antenna polarization is circular in this frequency range. The designed antenna is light, low-cost and easy to manufacture and therefore can be conveniently used as reader antenna in RFID retail monitoring applications.

Fiber-Based SPR Sensors with Calibration Function

This work was to introduce a reference mechanism in fiber based-SPR (surface plasmon resonance) sensors to increase their sensitivity. We fabricated two tandem SPR sections in a single optical fiber and coated one of the sections with a reference material to split a regular single resonant peak into two peaks, one in regular wavelength range for sensing and another one in longer wavelength range for referencing. By using the referencing peak to specifically detect the SPR changes caused by uncontrolled factors, such as temperature variation, non-specific bonding, we were able to subtract the contribution of these factors to the sensing peak using an established relationship, and thus increase the sensitivity of the sensing dip. With the method, we have demonstrated a fiber-based SPR humidity sensor whose sensitivity is immune to the variation of environment temperature.

Calculate BER Improvement due to Nonlinear Regenerators

Use the method developed recently we calculate the bit-error-rate (BER) improvement as a function of transmitter extinction ratio and the optical link noise parameter.

Quantum algorithm for designing multi-reflector resonant bandpass filters

Quantum operator algebra related to Jaynes-Cummings model is developed to design multi-reflector resonant bandpass filters for the first time. Transmittance and reflectance spectra of these filters are givens with analytic expressions. The results are found in agreement with those based on the existing filter design method. By selecting parameters such as r and N, designed filters can achieve a target spectrum profile with flat-top, large bandwidth, and minor ripples.

Erratum to "High-Power Multiwavelength Er

Due to a production error in the above-named paper [ibid., vol. 17, no. 9, pp. 1821?1823, Sep. 2005], Fig. 4 was printed twice. The correct Figs. 3 and 4 are provided.

^3+

The spontaneous emission spectrum of a ladder three-level atom with an upper transition driven by a coherent field is calculated under a universal model where various decays, any incoherent pumping and coherent driving are taken into account. The analytical expression for the spectrum profile is given on the basis of the quantum regression theorem. To our knowledge, it is the first time that the quantitative criterion condition Ω<|γab−γac|, under which quantum destructive interference induced by the coherent driving field occurs, is deduced for the modification of spontaneous emission from the middle level to the ground level. The roles and limits of incoherent pumping, coherent driving and experimental configuration are discussed for realizing the quantum interference and reducing the Doppler effects.