The relation between the phase shift and the mean optical power (MOP) output from a delay-line interferometer (DLI) port applied for phase-shift keying (PSK) signal demodulation is proven of a cosine law irrelevant to signal modulation condition. The variation amplitude of the MOP is proportional to the transition duration of the modulation pulses. This phenomenon is interpreted as the result of the statistical and waveform characteristics of the PSK. The conclusions verified by simulation and experiment are generalized to other modulation formats and then applied to phase detuning monitoring, delay time judgment of DLI, and independence of modulation data assessment.

In this letter, we propose and demonstrate a simple and novel method for fiber chromatic dispersion (CD) measurement based on microwave photonic technique. The radio frequency (RF) signal is modulated simultaneously on two light-waves with different wavelengths, and the light-wave carrying RF signals transmit through the dispersive medium under test. CD can be obtained by monitoring the power changing of the interference RF signals after photo detector. The CD values of the single-mode and dispersion compensation fibers are both measured within the wavelength range from 1 525 to 1 605 nm, which verifies the feasibility of this method.

A novel temperature-insensitive strain sensor, based on an in-line Mach-Zehnder interferometer, is fabricated by concatenating two waist-enlarged fiber tapers separated by a short piece of photonic crystal fiber. The interference spectrum of the proposed sensor is analyzed in detail. Experimental results demonstrate that this sensor has a strain sensitivity of 3.02 pm/\mu \varepsilon and maintains the temperature insensitivity feature. The proposed sensor has great potential in diverse sensing applications due to its advantages, such as its compact size, low cost, and simple fabrication process.

A Sagnac loop filter with two pieces of high birefringence fiber having equal lengths, and spliced together at a fixed angle of 30o displacement between the two principle axes, is proposed in this letter. Gain equalization of erbium-doped fiber amplifiers (EDFAs) is implemented by tuning only the polarization controller in the loop filter. Experimental result shows that there remains a deviation of \pm 1 dB in the region of the flattened profile with the useful bandwidth of about 23 nm, thereby demonstrating the effectiveness of the method. An effective mathematical model and mechanism is also given for further explanation.

The generation of coherent optical subcarriers based on a concatenated dual-drive Mach-Zehnder intensity modulator (IM) and two phase modulators (PMs) is proposed and experimentally demonstrated. The modulation index and DC bias of PM+IM modulation are theoretically investigated. Theoretical analysis and numerical study are also carried out to examine the proposed scheme. We use 25-GHz RF synchronous sinusoidal signals to drive cascaded two-stage PMs and IM, through which we generate 28 subcarriers with peak power fluctuations less than 4 dB. The measured tone-to-noise ratio of the subcarrier is higher than 40 dB. The experimental results show that for 100-Gb/s polarization multiplexing QPSK signal, the receiver sensitivity of the back-to-back signal is -28.6 dBm, and the power penalty is lower than 1 dB after 100-km transmission at the BER of 1 \times 10^{-9}.

A novel scalable and integrated design that supports optical multicast and burst amplification is proposed and demonstrated experimentally. The powers of incoming signals can be tuned to optimize the results of burst amplification and replication. Experimental results also show that erbium-doped optical Fiber amplication (EDFA) transients can be suppressed to an equally low level regardless of the burst parameters. Extended structure designs are further proposed to satisfy the need of mass replication of multicast signals.

A micro Fabry-Perot interferometer (M-FPI) is constructed by splicing a short section of polarization-maintaining photonic crystal fiber (PM-PCF) to an end-cleaved single-mode fiber with controllable offset. Due to the high effective optical path difference induced by the solid core of the PCF, the M-FPI has an ultrasmall cavity of approximately 110 \mu m. The temperature sensitivity within a range from 33 oC to approximately 600 oC is measured to be 13.8 pm/oC, which shows good agreement with the theoretical result. This proposed sensor has the advantages of ultracompact size and high stability. Therefore, it is suitable for various space-limited sensing applications in harsh environments.

Pulse position modulation (PPM) is introduced downstream of the reflective semiconductor optical amplifier (RSOA)-based single-fiber full-duplex bidirectional wavelength division multiplex passive optical network (WDM PON) to suppress the interference brought by the remodulation effect in the RSOA, Rayleigh backscattering, and reflection of the connection devices. In addition, because of the power-efficient characteristic of the PPM-encoded signals, the power budget shows clear improvement. As the experimental tests indicate, with ~6 dB extinction ratio (ER) in the downstream signal, the receiving sensitivity of the PPM-encoded channel is ~2.6 and ~3 dB higher than that of the NRZ (Non-return to zero)-encoded channel in the downlink and uplink, respectively.

A modal interferometer is experimentally demonstrated based on tapering a single-mode-multimode-single-mode (SMS) fiber structure heated by hydrogen flame. The interference fringe begins to form when tapering length is 19.8 mm, and becomes regular and clear when the tapering length is longer and the tapered waist diameter is smaller. Annealing process is undertaken to achieve a high extension ratio of approximately 17 dB with free spectral range of 1.5 nm when the tapering length is 33 mm and the tapered waist diameter is approximately 5 \mu m. The temperature and axial strain dependences of the tapered SMS structure are characterized, and the measured temperature and strain coefficients are +7 pm/oC and –9.536 pm/\mu \varepsilon, respectively.

We present a near diffraction-limited 1 064-nm Nd:YAG rod laser with output power of 82.3W(M2 \approx 1.38). The power fluctuation over two hours is better than \pm 1.1%. Pulsed 1 064-nm laser with an average power of 66.6 W and pulse width of 46 ns are achieved when the laser is Q-switched at a repetition rate of 10 kHz. The short pulse duration stems from the short cavity as well as the high-gain laser modules. Using intracavity-frequency-doubling, a 35.0-W near diffraction-limited 532-nm green laser (M2 \approx 1.32) is achieved with a pulse width of 43 ns.

We report the demonstration of passively continuous-wave mode-locking (CWML) of diode-pumped Tm,Ho:YVO4 laser using an InGaAs/GaAs multiple quantum-well (MQW) structure semiconductor as the saturable absorber. Stable mode-locking pulses at the central wavelength of 2 041 nm are obtained. The maximum output power is 151 mW. The pulse duration is 4.7 ps at the repetition rate of 64.3 MHz.

We investigate the spectra and scintillation properties of Ce:YAlO3, Ce:Y3Al5O12, and Ce:LaAlO3. For Ce:YAlO3, the excitation spectrum is very similar with the absorption spectrum; for Ce:Y3Al5O12 and Ce:LaAlO3, the excitation spectra are different from the absorption spectra. Further, Ce:YAlO3 has better scintillation performance than Ce:Y3Al5O12; whereas Ce:LaAlO3 has not demonstrated scintillation performance to date. We also provide reasonable explanations for these experimental phenomena from the viewpoint of energy level structure.

The structural and spectroscopic properties of Na2O-Al2O3-SiO2-xP2O5 glasses (x=0 to 7 mol%) are investigated. Both Raman and IR spectra reveal that discrete phosphate species ([PO4]^{-3}, [PO3O_{1/2}]^{-2}) with low polymerization degree can be formed in the silicate glass. These phosphate structures scavenge non-bridging oxygen ions and cations from the silicate network, resulting in an increase of the glass transition temperature. According to the Judd-Ofelt intensity parameters (\Omega2;\Omega4;\Omega6) of Er3+, the asymmetry of local environment around Er3+ becomes higher, and the bond covalency between Er3+ and O^{2-} decreases after P2O5 is introduced. In the emission spectra, photoluminescence intensity increases with increasing P2O5 concentration and the spectra are inhomogeneously broadened, revealing that the ligand electric field around Er3+ is dramatically changed, and the glass matrix becomes disordered.

Intense 2.7-\mu m emissions are obtained from Er3+/Nd3+ co-doped tellurite glass samples under the 808-nm laser diode excitation. According to the absorption spectra, Judd-Ofelt parameters and radiative transition probabilities are calculated and analyzed using the Judd-Ofelt theory. The spectroscopic properties and energy transfer mechanism between Er3+ and Nd3+ are analyzed. The effects of OH content on the spectroscopic properties of Er3+/Nd3+ co-doped samples are discussed. The obtained results indicate that Er3+/Nd3+ co-doped tellurite glass can significantly develop optical properties of 2.7-\mu m emission, if OH groups can be effectively eliminated.

Wave propagation is studied in structures consisting of alternate left- and right-handed layers. Bragg gap and zero-n gap appear in different frequency regions of the structure. The periodicity of the structure is broken by simply reversing the order of the layers in one half of the structure, resulting in defect modes located inside the zero-n gap and Bragg gap. These modes can be made very narrow by adding more layers in the structure. The defect mode located inside the zero-n gap is sensitive to the symmetry of the structure and insensitive to the angle ofincidence of the incoming radiation. Multiple modes are also generated inside the gaps by repeating the structural pattern. Thus, a simple structure can be used for single and multiple modes that are important for different applications.

Based on the concept of complementary media and theory of coordinate transformation, a novel kind of optical device, exhibiting the multiple performances of a complementary cloak and a transparent device, is proposed. Only the axial material parameter of the proposed device is spatially variant, and the transverse material parameters are constant. The multiple functions of the proposed device are validated by full wave simulations. In addition, the effects of loss and parameter perturbations on the performances of the device are also investigated. These results can be used in field of antenna protection and other electromagnetic field engineering.

Sensitized-emission fluorescence resonance energy transfer (FRET) detection method based on three-channel fluorescence microscopy is widely used. Several FRET algorithms, such as NFRET, FRETN, FR, FRETR, and FC/Df, are developed recently to quantitatively gauge and compare FRET signals between different experimental groups. However, the algorithms are difficult to choose and interpret. In this letter, we optimize the suitable yellow fluorescent protein (YFP) to cyan fluorescent protein (CFP) concentration ratio range for the above FRET algorithms. We also test the effect of YFP-to-CFP concentration ratio on the calculated energy transfer efficiency E and use the optimized FRET algorithms in the analysis of fas-associated protein with death domain (FADD) self-association directly in living cells.

Nonlinear absorption of monolayer graphene suspension is studied in the wavelength of 800 nm using Z-scan method with 50-fs pulses. Nonlinear absorption property of graphene suspension at different excitation intensities is compared. Large reverse saturable absorptions are found and believed to arise from twophoton absorption.

A convex aspheric surface using a computer-generated hologram (CGH) test plate fabricated with novel techniques and equipment is tested. However, the measurement result is not verified via comparison with other methods. To verify the accuracy of the measurement, a perfect sphere surface is measured by the following. The measurement result is quantified into four parts: the figure error from the tested spherical surface; the figure error from the reference spherical surface; the error from the hologram; and the adjustment error from misalignment. The measurement result, removed from the later three errors, shows agreement to 4-nm RMS with the test by Zygo interfermeter of the same surface. Analysis of the CGH test showed the overall accuracy of the 4-nm RMS, with 3.9 nm from the test plate figure, 0.5 nm from the hologram, and 0.74 nm from other sources, such as random vibration, various second order effects, and so on. Thus, the measurement accuracy using the proposed CGH could be very high. CGH can therefore be used to measure aspheric surfaces accurately.

A two-wavelength sinusoidal phase-modulating (SPM) laser diode (LD) interferometer for nanometer accuracy measurement is proposed. To eliminate the error caused by the intensity modulation, the SPM depth of the interference signal is chosen appropriately by varying the amplitude of the modulation current periodically. Then, the refine theory is induced to the measurement, and the two-wavelength interferometer (TWI) is combined with the single-wavelength LD interferometric technique to realize static displacement measurement with nanometer accuracy. Experimental results indicate that a static displacement measurement accuracy of 5 nm can be achieved over a range of 200 \mu m.

A two-step method for pose estimation based on five co-planar reference points is studied. In the first step, the pose of the object is estimated by a simple analytical solving process. The pixel coordinates of reference points on the image plane are extracted through image processing. Then, using affine invariants of the reference points with certain distances between each other, the coordinates of reference points in the camera coordinate system are solved. In the second step, the results obtained in the first step are used as initial values of an iterative solving process for gathering the exact solution. In such a solution, an unconstrained nonlinear optimization objective function is established through the objective functions produced by the depth estimation and the co-planarity of the five reference points to ensure the accuracy and convergence rate of the non-linear algorithm. The Levenberg-Marquardt optimization method is utilized to refine the initial values. The coordinates of the reference points in the camera coordinate system are obtained and transformed into the pose of the object. Experimental results show that the RMS of the azimuth angle reaches 0.076o in the measurement range of 0o-90o; the root mean square (RMS) of the pitch angle reaches 0.035o in the measurement range of 0o-60o; and the RMS of the roll angle reaches 0.036o in the measurement range of 0o-60o.