Erbium doped fiber ring laser for optical wavelength conversion

We experimentally investigate the gain saturation effect of a piece of 8 m long Erbium doped fiber (EDF), we introduce a theoretical model for the EDF ring loop, and our simulation results show very good cross-gain modulation (XGM) and wavelength conversion. We also experimentally investigate the XGM in an EDF ring loop system. Based on the study of the XGM in the EDF ring loop system, a wavelength conversion is designed with the EDF ring loop system. The EDF ring loop systems as a wavelength conversion is experimentally demonstrated by converting a sinusoidal modulated optical signal at wavelength of 1551 nm to an optical signal at wavelength of 1553.3 nm.     

A high flattening C + L band broadband source based on single pump and the same erbium-doped fiber

In order to realize a high flattening C + L band amplified spontaneous emission (ASE) light output, a broadband source using just one 976 nm laser diode (LD) and two stages erbium-doped fibers (EDF) with the same concentration is proposed theoretically and demonstrated experimentally, and the theoretical analysis and experimental verification are presented in details. Firstly, based on the energy level of Er³⁺, the methods of realizing C + L band ASE output is presented. Then, the system configuration is designed. One 976 nm LD is used for pumping, and the pump light, which is divided into two parts by one coupler, is pumped into two EDFs by wavelength division multiplexer (WDM). A fiber loop mirror (FLM) is used to improve working efficiency. Meanwhile, an optical isolator is used to avoid the effect of reflected wavelength from output facet. Finally, based on the mathematical model of the ASE gain, the length of EDF is discussed as well. In the experiment, by optimizing the length of EDF1 and EDF2, a 0.12 m EDF1 and 16 m EDF2 are adopted. In the end, the flatness of the spectra from 1540 nm to 1610 nm is ±0.91 dB, and the flatness is ±1.65 dB during 1520–1610 nm without any filter. The high flattening C + L band ASE output is achieved by just one 976 nm LD, which can optimize system and reduce the cost as well.     

Tunable dual wavelength fiber laser incorporating AWG and optical channel selector by controlling the cavity loss

In this paper, we propose and demonstrated a dual wavelength fiber laser (DWFL) based on the use of an erbium doped fiber (EDF) gain medium as well as an 1 × 24 Arrayed Waveguide Grating (AWG) together with two optical channel selectors (OCS) to provide channel spacing tunability. The output power of the two wavelengths is equalized by controlling the cavity loss in the DWFL using two Programmable Optical Attenuators (POAs). The widest spacing obtained from the DWFL is 18.13 nm while the narrowest spacing is 0.8 nm. The DWFL has good stability with only minor power fluctuations of less than 1.5 dB and a Side Mode Suppression Ratio (SMSR) of approximately 69.1 dB with peak fluctuations of less than 2.3 dB.     

Space radiation effect on EDFA for inter-satellite optical communication

The erbium-doped fiber (EDF) has been irradiated by electron with a dose of 1000 krad to analyse the space radiation effect on EDF amplifier (EDFA) in inter-satellite optical communication. This is the first work to analyse the effect on actually applied systems. Three critical parameters of EDFA, most important for external module subsystems, have been tested. The output power comes down to −57.21 dBm and the noise figure (NF) climbs up to 18.14 dB at dose 1000 krad, when the input power is −2.00 dBm. Although there is a strong ability to recover after the radiation experiment, EDFA deterioration is really huge. Apart from that, the central wavelength of EDFA never changes. To guarantee the accuracy of analysis of the radiation effect on EDFA, WDM coupler and isolator are also irradiated with the EDF at the same time. According to the results of all the tests, the EDFA could be directly used in the low-radiation dose orbits if doses are less than 20 krad. And the radiation experiment data will also be a good reference for the design of the actual systems in inter-satellite optical communication with different dose orbits.     

Fiber Bragg grating strain sensor based on fiber laser

A study on fiber Bragg grating (FBG) strain sensor, based on erbium-doped fiber (EDF) laser, is presented. A strain-sensing element, FBG, also acts as the lasing wavelength selecting component. When strain is applied on the FBG, the laser cavity loss changes, leading to a modification of the laser transient. Strain measurements are obtained in the time domain by simply measuring the EDF laser build-up time. Relative variation in the build-up time of up to 190%, for a strain range from 0 με to 2350 με, is achieved with a resolution corresponding to a strain of better than 2.35 με. This study demonstrates a novel fiber sensor concept and the technical feasibility to develop fiber strain measurement.     

Stable single longitudinal mode fiber ring laser based on polarization maintaining erbium doped fiber

A stable single longitudinal mode (SLM) fiber ring laser that incorporates polarization maintaining erbium doped fiber (PM EDF) acting as gain medium and saturable absorber is proposed and demonstrated. Both theoretical deviation and experimental result prove that optical intensity is time invariant when the laser operates in single longitudinal mode, the SLM operation can be approximately verified by optical intensity analysis, which is practical to analyze longitudinal mode in the application of engineering. The linewidth of the fiber ring laser is measured by the delayed self-heterodyne interferometery, and an acousto-optic frequency shifter is employed to shift the lasing frequency and eliminate zero frequency interfere. The SLM operation is verified by the scanning Fabry–Perot interferometer, whereas the lasing frequency drift slowly during a period of 2 h, PM EDF is proved to be effective on suppressing mode hopping and selecting longitudinal mode.     

Switchable multi-wavelength erbium-doped fiber ring laser based on cascaded polarization maintaining fiber Bragg gratings in a Sagnac loop interferometer

A switchable multi-wavelength erbium-doped fiber (EDF) ring laser based on cascaded polarization maintaining fiber Bragg gratings (PMFBGs) in a Sagnac loop interferometer as the wavelength-selective filter at room temperature is proposed. Due to the polarization hole burning (PHB) enhanced by the PMFBGs, stable single-, dual-, three- and four-wavelength lasing operations can be obtained. The laser can be switched among the stable single-, dual-, three- and four-wavelength lasing operations by adjusting the polarization controllers (PCs). The optical signal-to-noise ratio (OSNR) is over 50 dB.     

Discrimination of strain and temperature based on a polarization-maintaining photonic crystal fiber incorporating an erbium-doped fiber

A simple sensing method for simultaneous measurement of temperature and strain is investigated by using a Sagnac fiber loop mirror composed of a polarization-maintaining photonic crystal fiber (PM-PCF) incorporating an erbium-doped fiber (EDF). Amplified spontaneous emission created by a pumped EDF is transmitted to a Sagnac fiber loop mirror. The interference between two counter-propagating signals in a Sagnac fiber loop mirror generates a periodic transmission spectrum with respect to wavelength. When external temperature is increased, the transmission peak power reduces because the amplified spontaneous emission of the EDF is decreased by the applied temperature change (0.04 dB/°C). The peak wavelength is shifted into the shorter wavelength because of the negative temperature dependence of the birefringence of the PM-PCF (0.3 pm/°C). As the applied strain increases, the peak wavelength of the transmission spectrum of the Sagnac loop mirror incorporating the EDF shifts into a longer wavelength (1.3 pm/με) because the phase change of the proposed sensing probe is directly proportional to the applied strain. The transmission peak power, however, is not changed by the applied strain. Since the source and the sensing probe are integrated, the overall system configuration is significantly simplified without requiring any additional broadband light source. Therefore, it is possible to simultaneously measure temperature and strain by monitoring the variation of transmission peak power and peak wavelength, respectively.     

Optimization of a Raman/EDFA hybrid amplifier based on dual-order stimulated Raman scattering using a single-pump

Based on dual-order stimulated Raman scattering (SRS) of a single 1395 nm Raman fiber laser in 75 km single mode fiber and its corresponding dispersion compensation module, a hybrid Raman/Erbium doped fiber amplifier (EDFA) for long wavelength band (L-band) amplification is realized by inserting a segment of EDF within the span. By comparing the performance of gain and noise in four hybrid amplifiers with different span configurations, we find that the distribution of the secondary L-band amplification obtained from the EDF along the link has a great influence on the performance of the hybrid amplifier. Both gain and noise performance of hybrid amplifier can be improved significantly by optimizing the location of the EDF. Moreover, we can extend the flat gain bandwidth from L-band to central wavelength band (C-band) plus L-band by recycling the residual first-order SRS to pump a segment of EDF with proper length.     

SOA-based actively mode-locked fiber ring laser by forward injecting an external pulse train

An actively mode-locked fiber ring laser based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) is demonstrated to operate stably with a simple configuration. By forward injecting an easily-generated external pulse train, the mode-locked fiber laser can generate an optical-pulse sequence with pulsewidth about 6 ps and average output power about 7.9 mW. The output pulses show an ultra-low RMS jitter about 70.7 fs measured by a RF spectrum analyzer. The use of the proposed forward-injection configuration can realize the repetition-rate tunability from 1 to 15 GHz for the generated optical-pulse sequences. By employing a wavelength-tunable optical band-pass filter in the laser cavity, the operation wavelength of the designed SOA-based actively mode-locked fiber laser can be tuned continuously in a wide span between 1528 and 1565 nm. The parameters of external-injection optical pulses are studied experimentally to optimize the mode-locked fiber laser.     

A dual pumped double-pass L-band EDFA with high gain and low noise

This paper presents an efficient pumping scheme for L-band erbium-doped fiber (EDFA) amplifier to reach high gain and low noise performance in a double-pass configuration. The main L-band amplifier is composed of two sections of EDFs. A 980 nm and a 1480 nm pump lasers are used to pump the first section of EDF bi-directionally. The generated backward C-band amplified spontaneous emission noise from this EDF is used to pump a subsequent un-pumped section of EDF. In the double-pass scheme, a narrow-band fiber Bragg grating at each channel wavelength is used to back-reflect the L-band signal to make it amplified twice by the pair of EDFs. Compared with its conventional counterpart, this new double-pass configuration provides a lower noise figure and a higher gain. The pump conversion efficiency can be improved by more than 50% in a 3-channel demonstration by using the proposed configuration.     

Remotely pumped hybrid double-pass L-band optical amplifier utilizing chirped fiber Bragg

This paper reported an investigation of remotely pumped double pass L-band amplifier with dispersion compensation technique. The proposed design used chirped fiber Bragg grating (CFBG) to reflect the amplified signal back into the active medium, compensate the effect of fiber dispersion and block the recycled forward amplified spontaneous emission (ASE) and the residual 1480 nm pump power. The characterization of the design was done experimentally. The gain is 37.5 dB and noise figure is 4 dB with best BER of 10⁻⁵² is achieved when the EDF is placed 150 km away from the transmitter and 48 km before the receiver terminal.     

Optically controllable variable fiber optical attenuator integrated in conventional optical fiber

New type of optically controllable variable fiber optical attenuator based on thermo-optical effect in liquid cladding of optical fiber is described. The thermo-optical effect in liquid cladding optical fiber causes refractive index contrast changes in core–cladding interface, what enables to change the propagating optical signal power with temperature. The temperature change is achieved by fiber based heating element using laser radiation. Attenuation up to −12 dB was achieved in static dependence and dynamic response confirmed rise time up to 24 ms.     

Experiments of all-optical switching due to cross-phase modulation in fiber grating coupler by lock-in amp. detection scheme

We report results of experiments examining cross-phase modulation effect on fiber grating coupler (FGC). All-optical switching are observed in both cases of high pump pulses emitted from high-power Nd:YAG laser and mode-locked EDF laser. Based on coherent detection using a lock-in amplifier, the red-shift of the Bragg wavelength for a FGC was estimated to be 0.04-0.06 nm/1.5-1.7 kW peak power of EDF pump light at 1.55 μm. To avoid mixture of pump pulse and signal light at 1.55 μm, we have also performed the experiment using high power Nd:YAG laser as a pump power. For a Nd:YAG laser, the red-shift of Bragg wavelength is estimated to be 0.06 nm at maximum pump power of 2.1 kW. A simple model for the proposed detection scheme is given and the resultant red-shift is analyzed numerically.     

Variable optical attenuator based on a vertical comb drive actuated MEMS micromirror

This letter presents the design, simulation, fabrication, and successful demonstration of a variable optical attenuator (VOA) based on a micromachined micromirror combined with an optical fiber collimator. The micromirror has a size of 500 μm in diameter and a rotational resonance of 4.94 kHz. The micromirror was actuated by vertical comb drive which was fabricated by bulk micromachining process on a silicon on insulator (SOI) wafer. The VOA operates at a low driving voltage of 4.4 V corresponding to the rotation angle of 0.3°. The turn-on and turn-off response time of the VOA are 1.6 ms and 2.74 ms, respectively. Finally, the optical attenuation was measured and an optical attenuation as large as 40 dB was obtained.     

Multiwavelength fiber laser using S-band erbium-doped fiber amplifier and semiconductor optical amplifier

A multiwavelength fiber ring laser that is based on an S-band erbium-doped fiber amplifier (EDFA) and a semiconductor optical amplifier (SOA) is developed. An optical switch is used to switch the multiwavelength fiber laser between S-band and L-band. This fiber laser can stably lase seven wavelengths in the S-band or 28 wavelengths in the L-band. Additionally, the lasing wavelengths with a signal-to-noise ratio of over 33 dB and a wavelength spacing of 100 GHz are demonstrated experimentally. The average powers of the lasing wavelength in the S-band and the L-band are −7.53 and −12.15 dBm, respectively.     

Gain-clamped dual-stage L-band EDFA by using backward C-band ASE

A dual-stage L-band gain-clamped erbium-doped fiber amplifier (GC-EDFA) by using backward C-band amplified spontaneous emission (ASE) is proposed. Compared with other similar GC-EDFAs, the proposed structure has higher and flatter clamped gain in L-band because of its optimal pump power and EDF length. The flatness from 1570 nm to 1600 nm arrives 0.77 dB, the bandwidth of 3 dB is more than 35 nm and the maximal input signal power arrives −15 dBm.     

Ultra-fast 160:10 Gbit/s time demultiplexing by four wave mixing in 1 m-long B2O3-based fiber

One meter-long spool of bismuth oxide-based fiber, with nonlinear coefficient of 1250 W⁻¹ km⁻¹, is used to realize an optical 160-to-10 Gbit/s demultiplexer based on four wave mixing. Bit-Error-Rate measurements demonstrate a demultiplexing penalty lower than 2 dB confirming the suitability of bismuth oxide-based fiber for 160 Gbit/s all-optical processing.     

Numerical design of high nonlinear coefficient of microstructure optical fibers

This paper presents a theoretical design of highly nonlinear microstructure optical fiber with dispersion-flat characteristics. The APSS™ 2.3 software based on the finite difference method with perfectly matched boundary conditions is used to simulate the properties of the proposed microstructure optical fiber. According to simulation, the proposed fiber warrants a high nonlinear coefficient of the order 41 W⁻¹ km⁻¹ and a low dispersion of 0.25 ps/nm/km at 1550 nm wavelength. It assumes a dispersion-flat characteristic of 0 ± 0.50 ps/nm/km in a 1450-1620 nm wavelength range centering 1550 nm wavelength with a modest number of design parameters.     

Research on the temperature characteristics of optical fiber refractive index

The delay of optical signal is determined by the refractive index and length of optical fiber, and temperature would have an intense influence on the index. To establish the relationship between refractive index and temperature, the temperature characteristics of refractive index was analyzed and the thermo-optical coefficient equation was derived according to the polarization of the induced electric dipole moment in SiO₂ optical fiber. A measuring system based on optical fiber delay was carried out to measure the index within the temperature range of −30 °C to 70 °C and the experimental result was compared with the theoretical result. The final result shows that the relationship between refractive index and temperature is linear in the temperature range of discussion.