一种高效率的L波段掺铒光纤ASE宽带光源

利用双程双向泵浦单级掺铒光纤的结构实现高效率的L波段掺铒光纤放大自发辐射输出,同时选择1480nm半导体激光器作为泵浦源,高掺杂铒光纤为增益介质,通过优化铒光纤长度,获得了在1566-1604 nm（38 nm）,自发辐射谱功率高于－16 dBm,总输出功率13.7 dBm的L波段掺铒光纤放大自发辐射光源.该光源结构相比于双程前向泵浦结构的L波段掺铒光纤放大自发辐射光源,其泵浦效率从11.8%提高到23.4%.     

Enhancement of pump conversion efficiency in preamplified L-band erbium-doped fiber amplifiers

A new configuration of L-band erbium-doped fiber amplifiers (EDFAs) is presented here. The system contains a double-pass L-band EDFA and an optical preamplifier. Different from conventional preamplified double-pass L-band EDFA systems in which only the forward ASE of the preamplifier is re-used as an auxiliary pump, the new system recycles the backward ASE of the preamplifier as well. Two kinds of main L-band EDFAs are studied, both of which include a section of un-pumped erbium-doped fiber placed in a loop reflector. An improvement of up to 110% in pump conversion efficiency is demonstrated with the proposed recycling of the backward ASE, with respect to the system without recycling.     

High gain L-band erbium-doped fiber amplifier with two-stage double-pass configuration

An experiment on gain enhancement in the long wavelength band erbium-doped fiber amplifier (L-band EDFA) is demonstrated using dual forward pumping scheme in double-pass system. Compared to a single-stage single-pass scheme, the small signal gain for 1580 nm signal can be improved by 13.5 dB. However, a noise figure penalty of 2.9 dB was obtained due to the backward C-band ASE from second stage and the already amplified signal from the first pass that extracting energy from the forward C-band ASE. The maximum gain improvement of 13.7 dB was obtained at a signal wavelength of 1588 nm while signal and total pump powers were fixed at -30 dBm and 92 mW, respectively.     

L波段高掺铒光纤超荧光光源

采用半导体激光二极管泵浦12cm长高掺铒光纤,在双程前向装置中,获得了10.8mW最大超荧光输出功率,斜率效率10.6%,在1553.1~1588.6nm接近36nm的范围内,功率抖动小于0.2dBm。作为比较,在相同实验条件下泵浦10cm长的高掺铒光纤,结果显示输出光谱带宽明显下降,C波段的放大自发辐射远大于L波段的,由此也证明了L波段的放大自发辐射是由C波段的放大自发辐射泵浦产生的。     

新颖的高功率L-波段掺铒光纤超荧光光源

研究了L-波段超荧光在光纤中的产生机理,设计了一种带光纤圈反射器的双级双程前向输出L-波段光源结构,通过对两级采用掺铒浓度不同的光纤并优化其长度及两级泵浦光功率,实验中获得了功率高达19.86mW(12.98dBm)、中心波长为1577.421nm的L-波段(1555-1620nm)超荧光光源。实现了低浓度掺铒光纤起诱导光及改善光谱的作用,高浓度光纤为主要发光源,采用光纤圈反射器提高了泵浦光的利用效率、光源的平坦度及稳定性。同时分析了结构中各个参量对光源各方面性能的影响,对光源的设计具有指导意义。     

一种高功率掺铒光纤超荧光光源

通过优化掺铒光纤各种参量,用一个980 nm激光二极管作抽运源,采用单程结构,在一根光纤后向获得功率高达31.74 mW(15.02 dBm)的C-波段ASE输出的同时,其前向得到了功率为10.14 mW(10.06 dBm)的L-波段ASE输出.通过简单连接组合可得到输出覆盖C＋L波段(1525~1620 nm)功率＞36 mW的掺铒光纤宽带光源.     

An experimental investigation of the gain spectrum of erbium-doped fiber amplifiers under various system configurations

The paper presents an experimental investigation of the gain spectrum of an erbium-doped fiber amplifier (EDFA) considering different system configurations, which include single-pass, double-pass, and double-pass with tunable band-pass filter (TBF). The role of TBF is to suppress the undesired amplified spontaneous emission (ASE). Both co- and counter-pumping schemes are considered with a 1480 nm laser diode as the pump and a suitable tunable laser source as the signal source. The results indicate that the signal achieves an average of 14 dB higher gain in the case of double-pass amplification with the implementation of a TBF. However, the pumping scheme hardly becomes of much importance in influencing the gain characteristics.     

Simulation analysis of one-stage C+L-band erbium-doped fiber ASE source with double-pass bi-directional pumping configuration

A new technique to generate a C+L-band flat amplified spontaneous emission (ASE) source in one-stage erbium-doped fiber (EDF) using bi-directional pumping configuration is analyzed. The simulation results show that the key point of obtaining flat C+L-band ASE spectrum in one-stage EDF is using a laser diode operated at 980 nm as backward pump source. ASE source with nearly 80-nm bandwidth can be obtained by means of selecting suitable fiber length and properly adjusting the ratio of forward to backward pump power.     

The L-band EDFA of high clamped gain and low noise figure implemented using fiber Bragg grating and double-pass method

The L-band erbium-doped fiber amplifier (EDFA) of low noise figure and high clamped-gain using gain-clamped and double-pass configuration is presented in this paper. A total of five different configurations of EDFAs by reflection scheme with single forward pumping schemes are examined and compared here. Among these configurations, we first find the configuration of 1480-nm pumped L-band EDFA with optimum gain and noise figure value. To further minimize the gain variation, a fiber Bragg grating (FBG) with 1615-nm center wavelength and 1-nm bandwidth is determined and added in double-pass L-band EDFA. The gain variation and maximum noise figure of EDFA while channel dropping is investigated. As the number of channel dropping from 32 to 4, the L-band type-A EDFA keep the variation of gain within 2.9 dB and the maximum noise figure below 5 dB with each channel’s input power of −23 dBm.     

37.2 dB small-signal gain from Er/Yb Co-doped fiber amplifier with 20 mW pump power

An efficient erbium–ytterbium-doped fiber amplifier (EYDFA) is demonstrated by forward and backward pumping a 3 m erbium/ytterbium co-doped fibers (EYDF) in single- and double-pass configurations using a 20 mW pump. At the input signal wavelength of 1536 nm, the forward- and backward-pumped double-pass amplifiers achieved a maximum low-signal gain of 37.2 and 28.6 dB and a corresponding noise figure of 5.4 and 10.8 dB, respectively. Whereas, the forward- and backward-pumped single-pass amplifiers (at the same wavelength) achieved a maximum low-signal gain of 20.0 and 22.2 dB and a corresponding noise figure of 4.6 and 10.3 dB, respectively. The double-pass design offers an economical solution to high-efficiency and high-gain optical amplifiers.     

Wavelength tunable erbium-doped fiber ring laser operating in L-band

We describe a novel erbium-doped fiber ring laser utilizing the backward amplified spontaneous emission (ASE) power as a secondary pump source so that it can operate in L-band stably. The output wavelength can be tuned in a wide range of 45 nm, from 1560 to 1605 nm. We also compared this scheme with the condition of not using the ASE as secondary pump source, and found this scheme could improve the performance of the laser when using the same components.     

Gain and gain-flatness improved photonic crystal fiber Raman amplifier based on a dual-pass amplification configuration with single pump laser

A gain and gain-flatness improved L-band dual-pass Raman fiber amplifier (RFA) utilizing a photonic crystal fiber (PCF) as gain medium is demonstrated. By introducing complementary gain spectra of typical forward and backward pumping single-pass RFA using the same PCF, we finally achieve average net gain level of 22.5 dB with a ±0.8 dB flattening gain in 20-nm bandwidth from 1595 nm to 1615 nm, which is rare in RFAs with only one single pump and no flattening filter. Compared with the single-pass pump configurations, gain level, flatness and bandwidth are greatly improved by using the dual-pass amplification configuration. The limitation of this configuration caused by multi-path interference (MPI) noise and stimulated Brillouin scattering (SBS) is also discussed.     

Double-pass ytterbium-doped fiber amplifier with high gain coefficient and low noise figure

We have proposed and demonstrated a double-pass ytterbium-doped fiber amplifier using an optical circulator and a fiber Bragg grating as reflector. When the signal has passed through the ytterbium-doped fiber once, it reflects off a 0.2-nm passive fiber Bragg grating filter. This reduces amplified spontaneous emission (ASE) noise from the first pass. The input signal light is amplified both forward and backward through ytterbium-doped fiber. With this double-pass configuration, 1053.15-nm unsaturated signal gain of 28 dB, gain coefficient of 1.1 dB/mW, and noise figure of less than 4 dB are achieved at 977-nm pump power of 68 mW. It is also found that this double-pass configure provides enhancing gain coefficient and improving noise figure by comparison with single-pass configuration.     

2 W Yb-doped double-clad fiber superfluorescent source with 42 nm 3 dB bandwidth

The output spectrum of Yb-doped double-clad fiber superfluorescent source (SFS) is tailored by placing a broadband dichroic mirror in the pump end of conventional single-pass forward configuration, which constitutes double-pass forward configuration. The 3 dB bandwidth is increased from 11 to 42 nm. A maximum output SFS power of 2.12 W and a slope efficiency of 43.2% are obtained. The double-clad fiber is 25 m and the pump power is adequate to saturate the fiber as far as the feedback-induced lasing appears.     

新颖的双通道输出高功率掺铒光纤宽带光源

在分析L波段放大自发辐射(ASE)谱产生原理的基础上,设计出一种新颖的双级结构掺铒光纤ASE宽带光源,该光源可在两个端口分别输出高功率的C波段和L波段的ASE谱.设计将C波段ASE谱注入到掺铒光纤中作为L波段ASE谱的二次抽运源,使得L波段ASE谱功率得到了有效提高.优化光源结构参量后从两个端口分别获得了12.97 dBm和12.81 dBm的C波段和L波段ASE宽带谱.将两个输出端口组合得到了功率为15.9 dBm,泵浦转换效率达到21.6%的C+L波段超宽带ASE光源.     

High-performance SOA-based multiwavelength fiber lasers incorporating a novel double-pass waveguide-based MZI

In this paper, using a direct double-pass and a novel isolator-assisted double-pass waveguide-based Mach-Zehnder interferometer (MZI), high-performance SOA-based multiwavelength fiber lasers (MFL) are proposed and demonstrated experimentally. The filtering characteristics of the proposed isolator-assisted double-pass MZI are analyzed and examined theoretically in comparison with those of the single-pass and direct double-pass MZI. Using a direct double-pass waveguide-based MZI with the single-pass free spectral range (FSR) of 43 GHz, up to 115- and 104-channel simultaneous oscillations spaced at 21.5 GHz in the L-band and C-band are obtained, respectively, with a power non-uniformity of less than 3 dB and an extinction ratio of ∼30 dB. To the best of our knowledge, it is the highest lasing-channel count that has been achieved from an SOA-based MFL. To enhance the extinction ratio while maintaining the FSR, the proposed isolator-assisted double-pass MZI is then utilized in the laser cavity, and a stable 55-wavelength simultaneous oscillation spaced at 43 GHz is accordingly achieved in C-band with an extinction ratio of higher than 50 dB. Compared with the lasing linewidth of 0.058 nm with the conventional single-pass MZI, narrower linewidths of 0.038 and 0.028 nm are obtained with the isolator-assisted and direct double-pass MZI configurations, respectively. The lasers are stable with a maximum power fluctuation per channel of less than 0.8 dB during an hour’s test.     

Double-pass erbium-doped zirconia fiber amplifier for wide-band and flat-gain operations

The double-pass erbium-doped zirconia fiber amplifier (EDZFA) is proposed and demonstrated to provide a wide-band amplification as well as flat-gain operation in both the C- and L-band regions using only a single-gain medium. The proposed amplifier utilizes an erbium-doped zirconia fiber (EDZF) with erbium ion concentration of 2800 ppm as a gain medium. The medium is fabricated in a ternary glass host, zirconia-yttria-aluminum codoped silica fiber through solution doping technique along with modified chemical vapor deposition (MCVD). Compared to a single-pass operation, the double-pass EDZFA shows a better gain performance. At input signal power of 0 dBm and the optimum EDZF length of 2 m, a flat gain of around 16 dB is achieved by the proposed double-pass amplifier with gain variation of approximately 2.5 dB throughout the wavelength range from 1530 to 1590 nm. However, the noise figure of the double-pass amplifier is slightly higher than that of the single-pass due to inefficient population inversion at the input part of the amplifier.     

High-power flat L-band erbium-doped fiber ASE source using dual forward-pumping scheme

We experimentally investigate a high output power L-band (1565–1605 nm) erbium-doped fiber amplified spontaneous emission (ASE) source using dual forward-pumping configuration. Such configuration allows high pumping-power operation and enhances the pumping efficiency. The high pumping efficiency of 36.1% is achieved for such ASE source with a mirror reflectance of 30%. The output power of about 72.2 mW and a linewidth of 40.8 nm with a power ripple of 0.7 dB are obtained without using any external spectral filters.     

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.     

Gain-clamping techniques in two-stage double-pass L-band EDFA

Two designs of long-wavelength band erbium-doped fiber amplifier (L-band EDFA) for gain clamping in double-pass systems are demonstrated and compared. The first design is based on ring laser technique where a backward amplified spontaneous emission (ASE) from the second stage is routed into the feedback loop to create an oscillating laser for gain clamping. The gain is clamped at 18.6 d B from -40 to -80 dBm with a gain variation of less than ±0.1 dB and a noise figure of less than 6 dB. Another scheme is based on partial reflection of ASE into the EDFA, which is demonstrated using a narrowband fiber Bragg grating. This scheme achieves a good gain clamping characteristic up to -12 dBm of input signal power with a gain variation of less than ±0.3 dB from a clamped gain of 22 dB. The noise figure of a 1580 nm signal is maintained below 5 dB in this amplifier since this scheme is not based on lasing mechanism. The latter scheme is also expected to be free from the relaxation oscillation problem.