Dongfang Jia

Precise Simultaneous Multiwavelength Tuning by Electrical RF Signals

A method of simultaneous precise multiwavelength tuning using electrical instead of mechanical control is proposed and experimentally demonstrated. This method is achieved by using a single-side-band modulator driven by electrical radio frequency (RF) signals. It is demonstrated that the multiwavelength signals can be simultaneously tuned in frequency by an amount equal to the frequency of the RF signal. A total of 32 wavelengths with a spacing of 100 GHz (i.e., 0.8 nm at the wavelength of 1550 nm) are simultaneously tuned from 4 to 12 GHz experimentally. In principle, the tuning resolution is determined by the resolution of the RF wave generator and the line width of the light source in the system. An acceptable homogenous 20.59-dB side-band-mode suppression ratio is achieved for each wavelength output.

Multi-wavelength lasers with suppressed spectral linewidth of 10 kHz

High coherent multi-wavelength or multi-tone light source are in high demand for optical density wavelength division multiplexed (DWDM) networks as the telecommunication capacity expands exponentially. However the linewidths of commercial multi-wavelength semiconductor lasers are typically a few MHz which is not acceptable when the frequency spacing of the multi-tones is 10 GHz. In this paper, a novel and simple method to suppress the linewidths of the multi-wavelength from ~6 MHz to ~10 kHz using an all-optical approach is proposed and demonstrated. The linewidths of the multi-wavelength are suppressed by a factor of 600 and the noise level of the multi-wavelength is decreased by nearly 20 dB. Each wavelength of the multi-wavelength operates in single longitudinal mode. Finally, more than 8 wavelengths over 10 nm are suppressed simultaneously through the approach and scheme presented in this work.

Ultra-wide square pulses generation in a Yb-doped fiber laser based on nonlinear polarization rotation effect

An ultra-wide square pulse is demonstrated in a passively mode-locked Yb-doped fiber laser based on nonlinear polarization rotation effect. In our experiment, the pulse width can be tuned from 26 ns to 164 ns without wave-breaking when the pump power increases from 210 mW to 600 mW. And the peak power of the square pulse remains constant. The maximum output single pulse energy is 8.75 nJ at a pump power of 600 mW. To the best of our knowledge, this is the widest pulse in any mode-locked Yb-doped fiber laser.

An FBG sensor interrogation technique based on a precise optical recirculating frequency shifter driven by RF signals

Fiber Bragg grating (FBG) sensors have numerous advantages to sense multi-physical quantities such as the temperature and strain simultaneously by monitoring the shift of the returned “Bragg” wavelength resulting from changes in these quantities. Several FBG interrogation systems have been set up using photo detectors instead of an optical spectrum analyzer (OSA) to convert wavelength to time measurements. However, in those systems, it is necessary to use mechanical tuning components to generate fast-speed wavelength-swept light sources for high-precision FBG interrogation. In this paper, a low-cost and delicate wavelength-shift detection system, without any mechanical scanning parts, is proposed and demonstrated. The wavelength scanning system is a recirculating frequency shifter (RFS) which consists of an optical amplifier, an under test FBG sensor and an optical single-sideband (SSB) modulator driven by RF signals at 10 GHz. The measurement accuracy of this system is 0.08nm.

An ultra-long cavity passively mode-locked fiber laser based on nonlinear polarization rotation in a semiconductor optical amplifier

In this paper we investigate an ultra-long cavity passively mode-locked fiber laser based on a semiconductor optical amplifier (SOA). Experimental results are presented which indicate that stable mode-locked pulses can be obtained by combining nonlinear polarization rotation (NPR) in the SOA with a polarization controller. By adding a 4 km single mode fiber into the ring cavity, a stable fundamental-order mode-locked pulse train with a repetition rate of 50.72 kHz is generated through the NPR effect in the SOA. The central wavelength, 3 dB bandwidth and single pulse energy of the output pulse are 1543.95 nm, 1.506 nm and 33.12 nJ, respectively. Harmonic mode-locked pulses are also observed in experiments when the parameters are chosen properly.

High energy passively mode-locked Erbium-doped fiber laser at tens of kHz repetition rate

We demonstrate an ultra-long cavity all-fiber Erbium-doped fiber laser that is passively mode-locked by nonlinear polarization rotation. The length of the resonant cavity amounts to 4.046 km, which is achieved by incorporating a 4 km single mode fiber. The laser generates stable mode-locked pulses with a 50.90 kHz fundamental repetition rate. The maximum average power of output pulses is 2.73 mW, which corresponds to per-pulse energy of 53.63 nJ.

Study on all-optical 2R regeneration at 40 Gbit/s based on SPM

In recent years, optical fiber communication system has made a great development, but the quality of the optical signal will be seriously deteriorated by some factors, such as amplified spontaneous emission (ASE) noise, group velocity dispersion and so on. The traditional regeneration technology is accomplished within the electrical domain, and the opticalelectrical-optical conversion consumes vast amounts of energy. So it is necessary for all optical regeneration technology. This paper introduces the principle of an all-optical 2R regenerator based on self-phase modulation(SPM) and offset filtering technology. The deteriorated optical signal at 40 Gbit/s has been regenerated by the combination of SPM in highly nonlinear fiber (HNLF) and offset filtering. The factors influencing the regeneration have been analyzed by changing related parameters. It is concluded that by reasonably choosing parameters, we can get the best result of all-optical 2R regeneration.

Generations of linear frequency modulation continuous

An external modulation technique for the generation of optical linearly chirped frequency continuous waves is proposed and experimentally demonstrated. The output from a distributed feedback (DFB) laser is modulated by a single sideband (SSB) modulator which is driven by a linearly chirped electrical signal generated by an arbitrary waveform generator (AWG). A high precise linear optical frequency sweep with a tuning range of 2.5GHz is successfully achieved. Due to the good modulation quality of SSB and high stability of AWG, the chirp of the electrical signal can be perfectly modulated onto the optical signal. The linearity of the optical signal is almost consistent with the linearity of the electrical signal. The best linearity of 0.9996 and the lowest jitter rate of 4.76 % are obtained from the experimental measurements which are reported in this paper.

Picosecond-pulse generation over 10 GHz repetition rate based on cascaded semiconductor optical amplifiers

A cavity-free setup to generate short pulses at high repetition rate is introduced, which is based on four-wave mixing (FWM) in cascaded semiconductor optical amplifiers (SOAs). High repetition rate picosecond-pulse is important in optical communication and all-optic information processing systems. Cavity-free setup based on SOA means without ring cavity, which is stable and easy to be large-scale integrated. In this paper, we obtain picosecond-pulse around 10GHz repetition rate and the side-mode suppression ratio is 23 dB. Moreover, the repetition rate and center wavelength of optical pulse is tunable.

External Modulation Method for Generating Accurate Linear Optical FMCW

Frequency modulation continuous wave (FMCW) lasers are key components in modern optical imaging. However, current intracavity modulation lasers do not exhibit low-frequency jitter rate and high linearity due to the inherent relaxation oscillations. Although this may be compensated in a direct modulation laser diode using an optoelectronic feedback loop, the available sweep speed is moderately small. In this letter, a special external modulation method is developed to improve the performance of FMCW. Since only the first sideband optical field is used during the entire generation process, phase noise is kept to a minimum and is also independent of the sweep speed. We demonstrate that the linearity and jitter rates do not deteriorate appreciably when the sweep speed is changed over three orders of magnitude, even up to the highest sweep speed of 2.5 GHz/