A High Efficiency L-band Erbium Doped Fiber ASE Broadband Light Source

Abstract: A double-pass bi-directional(DP_BD) pump configuration is proposed for the high efficiency L-band ASE. A L-band ASE of 13.7 dBm output power and 38nm bandwidth of 1566~1604 nm where the ASE power intensity is higher than -16 dBm is obtained by selecting 1480 nm LD and heavily doped erbium fiber with optimized length simultaneously. The DP-BD ASE source has a pump conversion efficiency of 23.4% which is larger than that by double-pass forward (DPF) configuration of 11.8%.

Introduction

Broadband light source based on erbium-doped fiber amplifying spontaneous emission (ASE) is a new type of light source with erbium-doped fiber amplifier (EDFA). Since the first commercial use of EDFA for all-optical amplification in 1993 has led to the rapid development of optical communication, broadband light sources based on erbium-doped fiber ASE have the same output spectrum as the 1.55" m-band of optical communication, and have The output spectrum is stable, the environment is small, the output power is high, and it is easy to couple with the fiber system. It has become an optical device (such as EDFA, fiber grating and other optical passive) in dense wavelength division multiplexing system (DWDM). Device) testing, fiber optic sensing and fiber optic gyro and access to the important source of spectrally split multi-wavelength light source applications have received great attention and extensive research. Currently, the communication bandwidth of DWDM systems has been from the original C-band ( 1525 ~ 1565nm) to the L-band (1565 ~ 1605 rim) expansion, therefore, L-band ASE broadband source research has received increasing attention. However, compared to the C-band ASE broadband source, L-band ASE source is relatively less research, its technology It is also less mature. In this paper, the power of the erbium-doped fiber ASE is weak in the L-segment, and it is proposed to simultaneously utilize the ASE of the erbium-doped fiber in both directions (ie, two-way) and utilize two pump lasers. A high-efficiency L-band ASE output is achieved by illuminating the erbium-doped fiber in two directions simultaneously (ie, bi-directionally pumping). Experimental results show that the DP BD configuration is better than the two-way forward direction. The pumping structure (DPF configuration) has higher pumping efficiency.

Basic principle

Figure 1 is a diagram of the erbium ion energy level. When the erbium-doped fiber is pumped by a 980 nm or 1480 nm laser, the number of particles will be reversed as the pump light is strengthened. The spontaneous emission of high-energy atoms is in the fiber. During medium propagation, it is continuously stimulated to amplify and form amplified spontaneous radiation. As shown in Figure 1, the formation of L-band ASE is the same as c-band ASE. The difference is that the L-band ASE is generated by the transition between the low energy level of the Stark splitting energy level of ‰ and 4I.5, 2 main energy levels. The formation of L-band ASE can be briefly summarized as follows: after the erbium ion absorbs the 980 nm or 1480 nm pump laser, the C-band ASE is first generated at the front end of the erbium fiber, and the generated c-band ASE is absorbed by the back-end erbium fiber as a second. The pump source thereby shifts the ASE spectrum onto the L-band to form I. Band ASE spectrum. Since the L-band amplified spontaneous emission uses the tail of the erbium ion gain band, its emission and absorption coefficients are 3 to 4 times smaller than the c-band. Although the amplified spontaneous emission coefficient of the L-band is much lower than that of the c-band, its gain is flat. Due to the low particle number distribution, the erbium-doped fiber required to obtain the L-band ASE is relatively long, which is about several times that of the C-band ASE at the same doping concentration. This inevitably increases the absorption loss of the fiber and the accumulation of the backward amplified spontaneous emission, which reduces the pump conversion efficiency. The use of highly doped and low-loss doped fibers reduces the required fiber length, reduces absorption losses, and accumulates back-amplified spontaneous emission, thereby improving pump conversion efficiency. In addition, the amplification of spontaneous emission efficiency is also related to the choice of pump source wavelength. The quantum efficiency of 1480 nm pump laser is higher than 980 nm. Selecting 1480 nm pump laser is more conducive to obtaining high efficiency. Band ASE source. Therefore, high-doped erbium fibers and 1480 nm pump lasers are usually selected simultaneously to obtain high-efficiency L-band ASE sources.

2  Experiments and Results

Figure 2 is a two-way bidirectionally pumped L-band erbium fiber ASE source structure. The pump source uses the 1480 nm semiconductor laser from Furukawa Corporation of Japan. The power of the 1480 nm laser is divided into two parts by forward and backward pumping of the same segment of erbium fiber, and the erbium fiber is used by Lucent. Highly doped erbium fiber, model LRL-EDF, with a cutoff wavelength of 1100 to 1400 nm, a mode field diameter of 5.2"m, a wavelength absorption of 17 to 33 dB/m at 1530 m, and a 10 dB absorption at 1200 nm. The km. two-way mirror is simply connected by a 3 dB coupler, and its reflectivity can reach more than 95% in both c-band and L-band. A isolators are connected to the output to avoid reflection and form a laser. In the experiment, the output spectrum and output power were measured with AN6317B spectrometer.

In the experiment, firstly study the L-band ASE source of the two-way forward structure (Figure 2, PB = 0). Directly connect the output of the 1480 nrn laser to the pump terminal of the pump coupler WDM1. The maximum output power of the 1480 nm laser is 100 mW. For the determined pump power, in order to obtain the best flatness L-band ASE spectrum, the EDF length has an optimal choice (ie, the best inverted particle number density); when the erbium fiber length is short, the L-band The tail of the spectrum is relatively low. At this time, the density of the inverted erbium ions is slightly larger. When the length of the erbium fiber is increased, the tail of the L-band ASE spectrum is gradually raised until the length of the EI)F is selected to the highest. Good value, at this time output the best flatness L-band ASE spectrum; when continue to increase the length of the bait fiber, because the pump power is not enough to produce a certain reverse particle number density, the resulting ASE is absorbed by the tail erbium fiber, resulting in ASE The spectral power drops. The lower ASE spectra of several different erbium fiber lengths were measured in the experiment. Figure 3(a) shows the ASE spectra measured by power pumping at EDF lengths of 19 m and 100 mW. It can be seen from the figure that at 1565 to 1607 nm (42 nm), the spontaneous emission spectrum power is higher than -- 21 (IBm, and has good spectral flatness, the spectrometer measured the ASE spectrum power is 10.7 dBm, the corresponding pump conversion efficiency is about 11.8%. Using a power divider to divide the power of 1480 nnl laser A part (50% in the experiment) was used as the backward pump (the total pump power was kept at 100 mw) to form the bidirectional pumping structure shown in Fig. 2. The ASE spectrum measured from the spectrometer was evident, except for ASE. The spectral output power becomes larger, and the spectral shape is almost the same as the two-way forward structure. As shown in Fig. 3(b), at 1566 to 1604 rim (38 rim), the spontaneous emission spectrum power is higher than 16 dBm. At 13.7 dBm, the corresponding pump conversion efficiency is 23.4%. It can be seen that the two-way bidirectional pumping structure has higher pump conversion efficiency than the two-way forward structure. In addition, the two-way pump one-way is also measured. In the case of the output of the ASE spectrum, the two-way mirror shown in Figure 2 was removed from the experiment. The measured ASE output spectrum is weak and the spectrum is not completely transferred to the L-band. That is, in a single pass case, a longer erbium-doped fiber is required to obtain a spectrally flat L-band ASE spectrum, and pump conversion The efficiency is also low. Generally speaking, in the L-band ASE source design, the two-way structure is commonly used.

3  Conclusions

In this paper, the two-way forward pump structure and the two-way bidirectional pump structure I are studied experimentally. The band ASE source shows that the two-way bidirectional pumping structure has higher pump conversion efficiency than the two-way forward pumping structure. At a pump power of 100 mW, an L-band ASE output of 13.7 dBm is obtained. At 1566 to 1604nm (38nm), the spontaneous emission spectrum power is higher than -16 dBm, and the corresponding pump conversion efficiency is 23.4%.