C-band ASE Research Articles

A bond-free PPLN thin film ridge waveguide

Lithium niobate thin film waveguide is attractive in nonlinear frequency conversion, especially in the second harmonic generation (SHG). However, the conventional fabrication method of lithium niobate thin film waveguide requires expensive bonding equipment and the prepared film is easy to peel off. In this paper, a novel fabrication method of PPLN thin film ridge waveguide with a trapezoidal substrate is presented, based on glue bonding. The PPLN waveguide together with its trapezoidal substrate is surrounded with low refractive glue to modulate the vertical refractive index gradient along the waveguide length, which was proved to be useful for broadband SHG with a theoretical bandwidth above 25 nm by changing the substrate thickness from 3 μm to 17 μm. The proposed structure was verified by using a C-band ASE laser as the pump source, where the SHG laser bandwidth is about 11 nm. The power of SHG is 2.55 μw, and the normalized conversion efficiency is 10.5 %/W∙cm2. This work is beneficial to simplify the fabrication process of lithium niobate thin film ridge waveguide, and has certain promotion significance for photonic chip integration.

High Efficiency Automatic-Power-Controlled and Gain-Clamped EDFA for Broadband Passive Optical Networking Systems

The configuration of a simple improved high efficiency automatic-power-controlled and gain-clamped EDFA (APC-GC-EDFA) for broadband passive optical networking systems (BPON) is presented here. In order to compensate the phase and amplitude variation due to the different distance between the optical line terminal (OLT) and optical network units (ONU), the APC-GC-EDFA need to be employed. A single 980 nm laser module is employed as the primary pump. To extend the bandwidth, all C-band ASE is recycled as the secondary pump to enhance the gain efficiency. An electrical feedback circuit is used as a multi-wavelength channel transmitter monitor for the automatic power control to improve the gain-flattened flatness for stable amplification. The experimental results prove that the EDFA system can provide flatter clamped gain in both C-band and L-band configurations. The gain flatness wavelength ranging from 1530 to 1610 nm is within 32.83 ± 0.64 dB, i.e. below 1.95 %. The gains are clamped at 33.85 ± 0.65 dB for the input signal power of −40 dBm to −10 dBm. The range of noise figure is between 6.37 and 6.56, which is slightly lower compared to that of unclamped amplifiers. This will be very useful for measuring the gain flatness of APC-GC-EDFA. Finally, we have also demonstrated the records of the overall simultaneous dynamics measurements for the new system stabilization. The carrier to noise ratio (CNR) is 49.5 to 50.8 dBc which is above the National Television System Committee (NTSC) standard of 43 dBc, and both composite second order (CSO) 69.2 to 71.5 dBc and composite triple beat (CTB) of 69.8 to 72.2 dBc are above 53 dBc. The recorded corresponding rise-time of 1.087 ms indicates that the system does not exhibit any overshoot of gain or ASE variation due to the signal at the beginning of the pulse.

Band-selective C- or L-band erbium-doped fiber amplified spontaneous emission source

Abstract. Two novel methods are demonstrated to build upa band-selective amplified spontaneous emission ASEbroadband light source that can operate in the selective con-ventional band C-band, 1525 1565 nm or long-wavelength band L-band, 1565 1605 nm region using a1 2 optical switch. With the backward ASE feedback tech-nique, an output power of 27.6 mW for the C-band ASE and11.8 mW for the L-band ASE are obtained while with thecompound pump technique, a power of 24.5 mW for L-bandASE and 27.2 mW for C-band ASE are obtained both with afixed total pump power of 100 mW. The advantage of usingthe backward ASE feedback technique is that the ASEsource design is simpler whereas the power of L-band ASEis lower, and the notable advantage of using the compoundpump technique is that the output powers of the two selec-tive bands C- or L-band are balanced though the configu-ration is a little complicated. © 2006 Society of Photo-Optical Instru-mentation Engineers. DOI: 10.1117/1.2171952 Subject terms: fluorescence; erbium lasers; opticalcommunications; fiber optics

L-band all-optical gain-clamped EDFA by utilizing C-band backward ASE

By using an optical circulator and C/L-band wavelength division multiplexer to recycle the C-band backward ASE, an L-band gain-clamped erbium-doped fiber amplifier is presented. We have experimentally studied the static gain clamping property of this amplifier. As the ASE feedback attenuation is set to 0, the gain at 1585nm can be clamped at 18.84±0.26dB within dynamic range of 25dB and the critical power reaches about −15.09dBm. The gain variation and saturated output power at 1585nm for 0dB attenuation are 1dB lower and 2.17dB higher than those for 30dB attenuation, which indicates that the L-band EDFA gain can be effectively clamped via the ASE injection technique.

Gain Improvement in Two-stage L-Band EDFA with Incorporation of Fiber Bragg Grating

The gain improvement in two-stage long wavelength band erbium doped fiber amplifier (L-band EDFA) is demonstrated by incorporation of broadband C-band fiber Bragg grating (FBG). The FBG is used to reflect the unwanted backward C-band ASE from second stage back into the system. The proposed technique has improved the small signal gain from 19.6 dB to 23.5 dB compared to those of an amplifier without the FBG. Besides gain improvement, this technique also reduces noise figure and the maximum noise figure improvement of 1.8 dB was obtained at input signal power of 0 dBm. At wavelength range from 1570 to 1600 nm, the gain of the proposed amplifier varies from 20.0 to 28.5 dB. The flat-gain is expected to be obtained by optimization of EDF length and pump powers. The corresponding noise figures are varied from 4.8 to 5.2 dB.

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.

Effect of injection of C-band ASE on L-band erbium-doped fiber amplifier

The effect of injecting conventional band (C-band) amplified spontaneous emission on the performance of long-wavelength band erbium-doped fiber amplifier (L-band EDFA) is demonstrated. It uses a circulator and broadband fiber Bragg grating (FBG) to route C-band ASE from a C-band EDFA. Injection of a small amount of ASE (attenuation of 20 dB or above) improves the small signal gain with a negligible noise figure penalty compared to that of an amplifier without the ASE injection. A maximum gain improvement of 3.5 dB is obtained at an attenuation of 20 dB. At very large amounts of ASE injection (attenuation of 0 dB), the gain of the amplifier is clamped at 15.2 dB from −40 to −10 dBm with a gain variation of less than 0.3 dB. The saturation power is also increased from −8 dBm (for without ASE injection) to 2 dBm (VOA=0 dB) with a slight noise figure penalty. These results show that the ASE injection technique can be used either for gain improvement or for gain clamping in L-band EDFA.

Gain-clamping in two-stage L-band EDFA using an unwanted backward ase from second stage

A gain clamping technique for the long wavelength band erbium-doped fiber amplifier (L-band EDFA) is presented. It uses two circulators and a broad band fiber Bragg grating to route wasted backward C-band ASE from the second stage and launch it back into the input end of the first stage of a two-stage amplifier. The two-stage L-band EDFA has shown a small signal gain improvement of 5.7 dB compared to a single-stage amplifier with a slight noise figure degradation. By utilizing the wasted backward ASE, a L-band gain-clamped EDFA with high gain can be realized. Compared to the unclamped case, this gain-clamping technique is effective in reducing the total gain variation as small as 0.3 dB .

Simple and efficient L-band erbium-doped fiber amplifiers for WDM networks

The performance of L-band erbium-doped fiber amplifier (EDFA) of a simple structure with a fiber Bragg grating (FBG) was investigated. The injected C-band ASE by the FBG offers low-cost amplification and greatly improves the efficiency of the EDFA. There are 9 and 4 dB improvements with the FBG at 1587 nm, at low and high input, respectively. The flat gain of 18 dB, up to a total input of −5 dBm at 150 mW of 980 nm pump, is obtained over 30 nm with less than ±0.5 dB gain variations without any gain equalizer. The proposed EDFA provides a cost-effective solution for wavelength division multiplexing systems.

Coupled structure for wide-band EDFA with gain and noise figure improvements from C to L-band ASE injection

We propose a novel structure for C plus L-band silica based wide-band erbium-doped fiber amplifiers (W-EDFA's), which use backward amplified spontaneous emission from the C-band EDFA as the pump-mediating injection source for the L-band amplifier unit. Experimental results show gain and noise figure improvements of over 2.6 dB and 0.6 dB, respectively, at -3.5 dBm of L-band input signal power. Spatially resolved numerical analysis confirms the pump-mediating effect of C-band backward ASE in the L-band EDFA for the gain and noise figure improvement, which also provides better understanding on the dynamics of C-band injection seed methods.