By optimizing the gain configuration and length of the loop, a 90-tone optical frequency comb (OFC) is successfully generated based on recirculating frequency shifter structure. The peak-to-peak power fluctuation of the 90-tone OFC is 4.26 dB and the tone-to-noise ratio is higher than 19.17 dB. To further analyze the noise accumulation feature of the tones when travelling around the loop, linewidth of the tones is measured by delayed self-heterodyne interferometer structure. The result shows the linewidth of the tones deteriorates little during the recirculating process, indicating that the generated OFC is an ideal multi-wavelength source for high-speed communication systems.

A novel method of measuring non-uniform strain along a fiber Bragg grating (FBG) using optical frequency domain reflectometry (OFDR) is proposed and experimentally demonstrated. This method can overcome the problems of traditional non-uniform strain measurement methods for FBGs, i.e., the likelihood of chirping and multiple peaking in the spectrum when FBG is subjected to inhomogeneous strain fields. Wavelength interrogation is realized by OFDR with a narrow-line-width tunable laser as the optical source. When non-uniform strain distributions along areas adjacent to structural damage are measured by this method, good agreement is obtained between measurements and theoretical simulation results.

The 10-Gb/s non-return-to-zero (NRZ) on-off-keying (OOK) data transmission over a 100-km transmission fiber link employing an all fiber 1.55-\mu m single longitudinal mode (SLM) distributed Bragg reflector (DBR) fiber laser as the signal source is demonstrated. The experimental result is comparable with that of the transmission system by using a commercially semiconductor distributed feedback (DFB) laser.

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}.

An approach to generate a flat optical comb with tunable comb spacing and adjustable comb number is proposed. In the proposed approach, a Mach-Zehnder modulator (MZM), being biased to generate two carrier-suppressed first-order sidebands, is cascaded with a phase modulator. The two optical sidebands are then sent to the phase modulator to generate two identical, but frequency-shifted phase-modulated spectra. Thanks to the complementary nature of the two adjacent comb lines in the phase-modulated spectra, the overlapping of the two spectra would lead to the generation of a flat optical comb. Since only the phase modulation index or the microwave power is needed to be adjusted, the system is easy to be implemented with tunable comb spacing and adjustable comb number. Numerical simulations are performed, and the approach is verified by an experiment.

Single-mode, long-wavelength vertical-cavity surface-emitting lasers (VCSELs) in the near- to mid-infrared covering the wavelength range from 1.3 to 2.3 \mum are presented. This wide spectral emission range opens applications in gas sensing and optical interconnects. All these lasers are monolithically grown in the InGaAlAs-InP material system utilizing a buried tunnel junction (BTJ) as current aperture. Fabricated with a novel high-speed design with reduced parasitics, bandwidths in excess of 10 GHz at 1.3 and 1.55 \mum have been achieved. Therefore, the coarse wavelength division multiplexing (CWDM) wavelength range of 1.3 to 1.6 \mum at 10 Gb/s can be accomplished with one technology. Error-free data-transmission at 10 Gb/s over a fiber link of 20 km is demonstrated. One-dimensional arrays have been fabricated with emission wavelengths addressable by current tuning. Micro-electro-mechanical system (MEMS) tunable devices provide an extended tuning range in excess of 50 nm with high spectral purity. All these devices feature continuous-wave (CW) operation with typical single-mode output powers exceeding 1 mW. The operation voltage is around 1－1.5 V and power consumption is as low as 10－20 mW. Furthermore, we have also developed VCSELs based on GaSb, targeting at the wavelength range from 2.3 to 3.0 \mum. The functionality of tunable diode laser spectroscopy (TDLS) systems is shown by presenting a laser hygrometer applying a 1.84-\mum VCSEL.

A spectrum-sliced multi-wavelength fiber source (SS-MWFS) based on double-pass superfluorescent fiber source (SFS) with a reflection Mach-Zehnder filter (RMZF) as the reflected comb filter is demonstrated. With backward pumped configuration, MWFS with 50 wavelength channels of extinction ratio (ER) of 16.7 dB is obtained over the almost total C-band gain region. Total output power of the MWFS is 16.2 mW which shows that a power of about 0.3 mW of per channel is achieved. The SS-MWFS with forward pumped configuration is also discussed for comparing. The backward pumped configuration can provide a larger output power while only a little smaller ER than that of the forward pumped configuration.

A broadband amplified spontaneous emission (ASE) source of 88 nm is demonstrated using novel bismuth-based erbium-doped fiber (EDF) with the length of only 49.2 cm in a bi-direction pumping scheme. The maximum output power of 14.3 dBm is obtained under total pump power of 162 mW. The fiber loop mirror which works as a broadband reflector is responsible for the broadband output spectrum of this source according to the experiments.

A novel tunable multi-wavelength fiber ring laser based on semiconductor optical amplifier (SOA) is proposed by using a high-birefringence (Hi-Bi) fiber loop mirror (FLM) as wavelength filter. With this configuration, the wavelength spacing of this laser can be varied by using the different lengths of Hi-Bi fiber. 8 wavelengths spacing on 450 GHz are experimentally obtained with more than 25-dB signal-to-noise ratio (SNR) for each channel using 1.28-m Hi-Bi fiber in Hi-Bi FLM. The output power variation between different channels is measured to be less than 5.9 dB. The linewidth of each channel is compressed from 0.347 to 0.186 nm by 1.5-m unpumped erbium-doped fiber (EDF). Meanwhile, 17 wavelengths spacing on ITU-gird (100 GHz) are also obtained with 5.9-m Hi-Bi fiber in Hi-Bi FLM. All these channels can be tuned together over 0.4 nm.