Timing jitter eater for optical pulse trains

Using a single phase modulator and dispersive fiber, we demonstrate a 12-dB reduction in the phase noise of a train of 6.5-ps pulses at a repetition rate of 10 GHz. A prechirp fiber is shown to improve performance.     

Timing jitter reduction in gain-switched VCSELs induced by external optical injection

A theoretical study of the effect of optical injection on the characteristics of pulses generated by gain-switched single and multimode VCSELs is performed. It is shown that a jitter reduction greater than 50% can be obtained with a slight increase in pulse width. Similar results are obtained for single and multimode emission when the light is injected in the dominant mode.     

Timing jitter induced by intrachannel interactions in optical fiber communication systems using CFG as dispersion compensator

In this paper, a theoretical model is proposed for the analysis of timing jitter induced by intrachannel interactions in optical fiber communication systems using chirped fiber grating (CFG) as dispersion compensator. And for the first time, the impact of group-delay ripple (GDR) on timing jitter is taken into account in detail, theoretically and numerically. Results show that the GDR may increase or decrease the timing jitter of certain pair of adjacent pulses, deciding by the ripple parameters. The maximum influence will be obtained when ripple period is about 2/5 of the input pulse width. In practical systems, the GDR enhance the timing jitter for some adjacent pulses while reduce it for some other adjacent pulses, depending on the pulse pattern and the GDR parameters. In our simulation, the GDR guarantees a 3.04 ps increase of the standard deviation of the timing jitter.     

Tunable erbium doped fiber ring laser using fiber Bragg grating-assisted add-drop filter

A stable and low costless tunable erbium doped fiber ring laser using fiber Bragg grating-assisted add-drop filter is proposed and demonstrated. A stable laser output is obtained with a 4 nm tuning range. The power fluctuation, full-width at half maximum and SMSR are measured to be less than 0.50 dB, smaller than 0.015 nm and better than 55 dB in this tuning range.     

Performance of Brillouin optical time domain reflectometer with erbium doped fiber amplifier

The performance of Brillouin optical time domain reflectometry (BOTDR) affected by different pump power and direction of erbium doped fiber amplifier (EDFA) is experimentally demonstrated. A temperature error of 0.5 °C and spatial resolution of 10 m is obtained over 80 km sensing fiber with EDFA. The temperature resolution and dynamic range of BOTDR with backward pumped EDFA is better than forward pumped EDFA. Within the range of pump power, the resolution of BOTDR can be improved by increasing pump power.     

Intensity based erbium distribution for erbium doped fiber amplifiers

A method to calculate an optimum Erbium distribution to enhance the gain efficiency in EDFA is proposed. This method calculates Erbium distribution based on optical pump envelop, pump power and optical properties of Erbium ion. The intensity-based Erbium distribution is obtained for single-mode fiber and dispersion-shifted fiber types EDFA for pump power from 10 to 40 mW. All of the profiles have a Gaussian-like shape. For single-mode fiber type EDFA, high gain enhancement is obtained in a relatively short optimal length of fiber. Optimal length of EDFA, using intensity-based Erbium distribution, is increased by a factor of 1.5–3 with respect to the one using stepwise. This optimal length increasing factor is considerably smaller than that of the EDFA, using the one-fourth confinement Erbium profile.     

Analysis of erbium doped holey fiber using fundamental space filling mode

Erbium-doped holey fiber with hexagonal lattice was modeled by using effective index method. In order to calculate the equivalent step index of the periodic structure of the cladding holey optical fiber, all-vectorial fundamental space filling mode approach was utilized. By using EH11 mode, we have numerically solved the rate equations of a three-level pumping scheme for a fiber laser. The obtained results have shown a good agreement with the other experimental results, recently. The results have predicted amplifiers with gain efficiencies as high as 10 dB/mW.     

Study of distributed erbium doped fiber amplifier

Basing on analyzing distributed erbium-doped fiber amplifier(d-EDFA) of evenly doped density along propagating direction, we put forward two sort d-EDFAs of slowly and linearly variously doped density along propagating direction: one-variation and two-variation d-EDFA. By using convective equations, we study the propagating properties of signal and noise in three sort d-EDFAs. Noise figure, signal-noise ratio, necessary pump and optimal pump period also are studied, under both transparent transmission and optimal doped density.     

重复频率可调谐的超低抖动光窄脉冲源的研究

提出了一种新型的基于光电振荡器的重复频率可调谐的超低抖动光窄脉冲源. 光电振荡器系统可以产生超低相位噪声的微波信号; 被该信号调制的直调光经过两次相位调制之后, 使光脉冲的啁啾增强; 再通过一段色散补偿光纤, 光脉冲被进一步压窄. 实验中使用YIG可调滤波器, 可以得到8–12 GHz内步进为200 MHz的可调谐微波信号, 因此光脉冲的重复频率具有可调谐性. 当微波信号即脉冲重复频率为9.6 GHz时, 测得脉冲宽度为3.7 ps, 相位噪声为-130.1 dBc/Hz@10 kHz. 由此得出光脉冲的瞬时抖动为60.1 fs (100 Hz–1 MHz), 因此该方案产生的光窄脉冲源具有超低的抖动.     

Side-polished fiber based gain-flattening filter for erbium doped fiber amplifiers

A simple and accurate novel normal mode analysis has been developed to take into account the effect of the non-uniform depth of polishing in the study of the transmission characteristics of optical waveguide devices based on loading of a side-polished fiber half-coupler with a multimode planar waveguide. We apply the same to design and fabricate a gain-flattening filter suitable for fiber amplifiers. The wavelength dependent filtering action of the overall device could demonstrate flattening of an EDFA gain spectrum within ±0.7 dB over a bandwidth of 30 nm in the C-band. Results obtained by the present analysis agree very well with our experimental results. This present analysis should be very useful in the accurate design and analysis of any SPF-MMOW device/component including side-polished fiber based sensors.     

Short optical pulse polarization dynamics in a nonlinear birefringent doped fiber

Numerical solutions are obtained of the full self-consistent system of equations for the counter, rotating polarization components of the field of a short optical pulse propagating in a nonlinear birefringent fiber and in the ensemble of the energy-level degenerate doped resonance atoms implanted in the fiber material. In every cross section of the fiber, the ellipticity of the polarized wave experiences a complex evolution in time accompanied by rapid changes of the azimuthal angle due to the interplay of the dispersion and the Kerr nonlinear self-and cross-phase modulation. The reciprocal effect of the impurities on the traveling pulse causes oscillations of the pulse envelope that can completely distort the shape of the input signal, while the resonance absorption can drive the birefringence process from the nonlinear regime back to the linear one.     

Luminescence properties of ytterbium and erbium doped silica-zirconia nanostructured optical fiber under near infrared excitation

We present here the luminescence properties of erbium and ytterbium doped silica-zirconia nanostructured optical fibers prepared by the chemical sol-gel method. After describing the preparation process, their waveguiding properties as well as luminescence properties under continuous pumping in the near infrared domain (NIR) are reported; the effects of the zirconia nanocrystals that are dispersed in the core of the fibers on their optical properties are finally discussed.     

Superluminal pulse propagation in an erbium fiber laser

It is well known that saturating gain media can give rise to superluminal pulse propagation velocity. In most mode-locked lasers the effect is unmeasurably small and has not yet been directly demonstrated. We present experiments on the initial transient of an erbium fiber laser that show a dynamic shift in the propagation velocity to a value larger than the medium’s linear group velocity as the pulse builds up. Received: 14 December 1998 / Revised version: 21 May 1999 / Published online: 25 August 1999     

Effects of geometrical parameters on optical characteristics of erbium doped photonic crystal fiber based on FVEIM

In this paper, using the fully vectorial effective index method (FVEIM), dependence of the refractive index of fundamental mode, mode field diameter and normalized frequency of the photonic crystal fiber on geometrical parameters of fiber are investigated. Simulations show that the normalized frequency of the photonic crystal fiber increases gently with increase of the air filling factor. Range of parameters in which erbium doped photonic crystal fiber is single mode at both the pump wavelength and the signal is determined. Wavelength dependence of the normalized frequency implies that single mode region of the signal in the case of using dopants such as ytterbium or erbium is significantly (about 1.6 times) more than the pump. In addition, it is shown that by changing dopant material to obtain a higher gain for an optimum set of geometrical parameters, no considerable change in the area of single mode occurs.     

Timing jitter reduction over 20-km urban fiber by compensating harmonic phase difference of locked femtosecond comb

A novel timing jitter reduction system over a round trip 20-km urban fiber link is reported. The phase difference of the ninth harmonic of a high-repetition-rate mode-locked laser between the local and the returned signals is obtained. Based on the phase difference, the system uses an optical delay line （ODL） to compensate the optical fiber link. The root-mean-square （RMS） timing jitter is reduced from 50 to 8.9 ps in 80 min.     

Optimization of core size in erbium doped holey fiber amplifiers

Holey fibers (HFs) can be used as amplifier in optical communication systems. These new fiber structures have flexibility to change the fiber parameters such as refractive index of guided mode, air filling factor (AFF), V number, group velocity dispersion (GVD) and numerical aperture, only by the change of the hole size and air-hole spacing. In this paper we will use improved fully vectorial effective index method (IFEIM) to analyze the erbium doped holey fiber amplifier (EDHFA) with hexagonal unit cell. The range that core size can change in any air-hole spacing will determine and the growth of core size in the amplifier character such as maximum gain and optimum length will study. By determination of single mode region the effect of pump power and dopant concentration growth, on the amplifier parameter will define.     

Timing jitter owing to intrachannel pulse interactions in dispersion-managed transmission systems

We study interaction-induced timing jitter in single-channel dispersion-managed return-to-zero ttransmission systems operating at high map strengths. An equation for the frequency and timing shifts of two interacting pulses is derived by a variational approach. The interaction can be of either an attractive or a repulsive character, and we show that the resultant timing jitter can be reduced by proper design of the dispersion map.     

Picosecond pulse amplification in a core-pumped large-mode-area erbium fiber

Amplification in a single-clad, large-mode-area erbium fiber as an alternative to double-clad Er-Yb amplifiers is presented. Both signal and pump are coupled through a mode-matched splice into the fundamental mode, which ensures preferential gain in the fundamental mode while minimizing the amplified spontaneous emission (ASE). The 875 microm(2) effective area of the Er fiber enables amplification of 6 ps pulses at 1.55 microm wavelength by approximately 33 dB in a single stage to >25 kW peak power with low nonlinear pulse distortion and a diffraction-limited output beam with M(2)<1.1.     

Stable mode-locked fiber laser using 49 cm long bismuth oxide based erbium doped fiber and slow saturable absorber

A stable mode-locked fiber laser employing a 49 cm long bismuth oxide based erbium doped fiber (Bi-EDF) by using a slow saturable absorber is demonstrated. Near transform limited short pulses with a repetition rate of 8.27 MHz are obtained at a wavelength of 1560 nm with a maximum spectral width of 15 nm. Results indicate that pulse characteristics are strongly dependent on pump power rather than spectral width. Moreover the Time-Bandwidth products (TBWP), pulse duration, the energy fluctuation and timing jitter decrease with increasing pump power. The pulse width is continuously varied from 1.2 ps to less than 300 fs. It produces stable mode locking with a maximum spectral width of 15 nm, minimum timing jitter of 4 ps and energy fluctuations of 2.5%. The pulse train was amplified using a two-stage amplifier up to 447 mW average power corresponding to peak powers of 177.3 kW.