Xuefang Zhou

Stable dual-wavelength single-longitudinal-mode ring erbium-doped fiber laser for optical generation of microwave frequency

We demonstrate a simple dual-wavelength ring erbium-doped fiber laser operating in single-longitudinal-mode (SLM) at room temperature. A pair of reflection type short-period fiber Bragg gratings (FBGs), which have two different center wavelengths of 1545.072 and 1545.284 nm, are used as the wavelength-selective component of the laser. A segment of unpumped polarization maintaining erbium-doped fiber (PM-EDF) is acted as a narrow multiband filter. By turning the polarization controller (PC) to enhance the polarization hole burning (PHB), the single-wavelength and dual-wavelength laser oscillations are observed at 1545.072 and 1545.284 nm. The output power variation is less than 0.6 dB for both wavelengths over a five-minute period and the optical signal to noise ratio (OSNR) is greater than 50 dB. By beating the dual-wavelengths at a photodetector (PD), a microwave signal at 26.44 GHz is demonstrated.

CW dual-frequency MOPA laser with frequency separation of 45 GHz.

A CW dual-frequency master oscillator power amplifier (MOPA) laser system with dozens of gigahertz (GHz) frequency separation is presented. The MOPA system consists of a monolithic microchip seed laser and a double-end pumped traveling wave power amplifier. The short length of seed laser cavity guarantees the seed signal with a large frequency separation (above 53 GHz) but low output power (below 247.8 mW). By adding a long and low-doped active medium laser amplifier stage, a significant increase in laser power and an improvement in beam quality are obtained. After fine temperature tuning of seed laser cavity for spectra matching, a 2.40 W dual-frequency laser signal with 45 GHz frequency separation is achieved.

Optical logic gates based on electro-optic modulation with Sagnac interferometer

In this work, we present a new structure to realize optical logic operation in a Sagnac interferometer with electro-optical modulation. In the scheme, we divide two counterpropagation signals in a Sagnac loop to two different arms with the electro-optical crystal by using two circulators. Lithium niobate materials whose electro-optical coefficient can be as large as 32.2×10(-12)u2009u2009m/V make up the arms of the waveguides. Using the transfer matrix of the fiber coupler, we analyze the propagation of signals in this system and obtain the transmission characteristic curves and the extinction ratio. The results indicate that this optical switching has a high extinction ratio of about 60 dB and an ultrafast response time of 2.036 ns. In addition, the results reveal that the change of the dephasing between the two input signals and the modification of the modulation voltage added to the electro-optical crystal leads to the change of the extinction ratio. We also conclude that, in cases of the dephasing of two initial input signals Δφ=0, we can obtain the various logical operations, such as the logical operations D=A¯·B, D=A·B¯, C=A+B, and D=A⊕B in ports C and D of the system by adjusting the modulation voltage. When Δφ≠0, we obtain the arithmetic operations D=A+B, C=A⊕B, D=A·B¯, and C=A¯·B in ports C and D. This study is significant for the design of all optical networks by adjusting the modulation voltage.

Tunable multiwavelength fiber laser based on a double Sagnac HiBi fiber loop

A tunable multiwavelength fiber laser based on double Sagnac loops is proposed and demonstrated. Comb filter characteristics of single and double Sagnac loops are analyzed by Jones matrix. Simulated results show that there are better tunability and controllability with double loops than with a single loop, and this also has been confirmed by experimental results. By adjusting the polarization controller and the length of the polarization maintaining fiber the wavelength range, wavelength spacing, and laser linewidth can be tuned. Experimental results indicate that the linewidth of the multiwavelength fiber laser was 0.0187 nm and the optical sidemode suppression ratio was 50 dB.

Dual-wavelength Brillouin ring-cavity fiber laser with tunable channel spacing

We experimentally demonstrate a dual-wavelength Brillouin fiber laser configured a pre-amplified Brillouin pump and FBG filter in a ring-cavity. The Brillouin laser can generate 21 Brillouin Stokes with 0.084 nm spacing, the first-Stoke has a peak power of 2.19 dBm. By adjusting the TLS wavelength and FBG’s reflection wavelength from circulating in the ring-cavity, the generated output dual-wavelength is stabile and the channel spacing is tunable, the widest and narrowest channel spacing obtained is approximately 1.12 nm (139 GHz) and 0.084 nm (10.5 GHz).

A Smooth and Gradual Evolution to Next Generation PON Based on Simple Line-Coding

We propose a smooth and gradual evolution method to next generation passive optical network (PON) based on simple line-coding. At the beginning, a new OLT and some new ONUs are added into the existing PON without changing the existing ONUs. The evolution is gradual. The existing ONUs can be upgraded with demand. The coding is operated by software and requires no extra equipment. During different evolution stages, different line-codes are applied to reduce the crosstalk induced by the upgrade service to the existing service. The crosstalk is tested and shown not serious in the experiment.

An optical add-drop multiplexer design based on fiber Bragg gratings

Optical add-drop multiplexers will play an important role in enabling greater connectivity and flexibility in dense wavelength-division multiplexing (DWDM) networks. In this paper, a reconfigurable optical add-drop multiplexer (OADM) architecture using a single multiport optical circulator (MOC) and several narrow band fiber Bragg gratings (FBGs) is proposed and demonstrated. The proposed OADM exhibits a lower insertion loss and lower through loss than existing OADMs. The proposed OADM may find important applications in DWDM systems and networks.

A Novel Switchable Dual-Wavelength Ring Erbium-Doped Fiber Laser Operating in single-longitudinal-mode

In this paper, we demonstrate a simple switchable dual-wavelength ring erbium-doped fiber laser operating in single-longitudinal-mode (SLM) at room temperature. A pair of reflection type short-period fiber Bragg gratings (FBGs) is used as the wavelength-selective component of the laser. A segment of unpumped polarization maintaining erbium-doped fiber (PM-EDF) is acted as a narrow multiband filter. By turning the polarization controller (PC) to balance the gain and loss in the ring cavity, single-wavelength and dual-wavelength laser oscillations are observed. The output power variation is less than 0.6dB for both wavelengths over a five-minute period and the optical signal to noise (ONSR) is greater than 50dB.

Wavelength tunable single freqeuncy bistability erbium-doped fiber ring laser

In this paper, a tunable single-frequency fiber laser is designed. For narrow linewidth and single frequency operation, a length of 2.75m unpumped EDF as a saturable absorber is used. The FBG combined with the unpumped EDF provides narrow frequency selection. Counter propagating beams in the unpumped EDF form a standing wave that results in periodic spatial hole burning. This creates a narrower bandwidth absorption grating than the FBG. The output laser wavelength can be changed from 1530nm to 1570nm by the FBG. The 3dB spectrum width of output laser is 0.08nm and the side mode suppression ratio is 55dB. The maximum output power exceeds 12mW, and the stability is less than ±0.005dB. A nice single-frequency laser is observed. From the relationship of the pump power and output power, it is obvious that the optical bistability switchable phenomena is showed in output characteristics. The bistability switchable phenomena is caused by the saturable absorber in the ring cavity. A 10Gb/s codes rate is used in the fiber laser transmission experiment. The high speed optical signal is transmitted in long distance without regeneration. The eye diagrams of optical transmission are measured, the performance of long haul transmission with high speed modulation is perfect.

Impairment-aware dynamic RWA algorithm in multi-granularity WDM optical networks

In practical multi-granularity WDM optical networks, optical signals will be degraded due to impairments mainly introduced by a number of multi-granularity optical cross-connects (MG-OXC) and fiber links. Even worse, transmission impairments will make the bit-error rate to be unacceptable. We investigate the impact of transmission impairments on optical signal quality in multi-granularity WDM optical networks. A novel dynamic impairment-aware RWA algorithm is proposed based on the presented transmission impairments model. We also evaluate the proposed algorithm in the serial cascaded MG-OXCs network and the interconnecting MG-OXCs network by simulations.