Showing papers by "Harith Ahmad published in 2002"

Gain enhancement in L-band EDFA through a double-pass technique

Abstract: An improvement of gain in the long-wavelength band (L-band) is observed by double passing the forward amplified spontaneous emission and signal in the erbium-doped fiber (EDF) using a circulator, unlike conventional single pass amplification. A gain enhancement as high as 11 dB is obtained for a 1570-nm signal with an input power of -20 dBm at 98 mW of pump power. However, a noise figure penalty of about 2 dB is observed.

Gain clamping in L-band erbium-doped fiber amplifier using a fiber Bragg grating

Abstract: A gain-clamping technique for the long wavelength band (L-band) erbium-doped fiber amplifier (EDFA) is presented. It uses a single fiber Bragg grating (FBG) on the input side of erbium-doped fiber (EDF) to inject a portion of backward conventional band (C-band) amplified spontaneous emission (ASE) back into the system. The use of a narrow-band (NB) FBG has shown a better performance in clamped-gain level and noise figure compared to a broad-band FBG. The amplifier gain for the NB FBG set up is clamped at 15.4 dB with a variation of less than 0.3 dB for an input power as high as 0 dBm.

Gain Control in L-Band Erbium-Doped Fiber Amplifier Using a Ring Resonator

Abstract: Gain control in a long-wavelength (L-band) erbium-doped fiber amplifier (EDFA) using a counter-propagating ring resonator is demonstrated. The clamped gain can be controlled to be in the range from 7.0 to 18.0 dB for the 1580 nm signal at -30 dBm by tuning the oscillating laser in the range from 1565 to 1540 nm. The design prevents oscillating light from being coupled out, but it degrades the amplifier's noise figure and signal gain as the dynamic range is increased.

Multiwavelength Laser Comb in L-Band Region with Dual-Cavity Brillouin/Erbium Fiber Laser.

Abstract: A dual-cavity Brillouin/erbium fiber laser (BEFL) demonstrates a multiwavelength output in the L-band region. The system consists of two erbium-doped fiber lasers (EDFLs) that share a length of the single-mode fiber (SMF) to produce a bidirectional Stokes signal. 2×10 lines including the anti-Stokes line with 22 GHz of wavelength spacing are obtained with maximum Brillouin and 980 nm pump powers of 4.8 mW and 92 mW, respectively. The BEFL has a broad tuning range greater than 10 nm. The laser comb has a potential application in future wavelength division multiplexing (WDM) systems.

Efficient multiwavelength generation of Brillouin/erbium fiber laser at 1600‐nm region

Abstract: An efficient Brillouin/erbium fiber laser, which operates in the 1600-nm (L-band) region, is demonstrated for potential applications in future dense-wavelength division multiplexing communication systems. The laser configuration consists of an L-band EDFA (to enable L-band amplification) where two 3-dB couplers take a portion of the generated BEFL signal and re-inject it into the single-mode fiber in order to seed a cascaded BEFL line in the same direction as the first BEFL line. An efficient BEFL can be obtained by recycling backward a 1550-nm-band amplified spontaneous emission as a secondary pump source for the unpumped EDF in the L-band EDFA section. As a result, the lasing threshold is reduced and slope efficiency is improved. A stable and strong laser comb of up to five lines with 10-GHz spacing has been obtained with a Brillouin pump of 4.8 mW and a 980-nm pump of 92 mW. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 506–508, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10650

A Gain-Clamped L-Band Erbium-Doped Fiber Amplifier Using Ring Laser Cavity with a Fiber Bragg Grating

Abstract: In this letter, a design of a gain-clamped long wavelength band erbium-doped fiber amplifier (L-band EDFA) is proposed using a fiber Bragg grating in a closed loop ring cavity. The design provides a clamping of the gain with different variable optical attenuator (VOA) losses varying from 0 to 12.5 dB. It is found that at 10 dB VOA loss, clamping of the gain is flat with variation of input power from -40 to -5 dBm. The gain measured is 10.9 dB, which is 30% less than the open ring gain of 15.3 dB at a pumping power of 92 mW. The noise figure measured is about 5.2 dB.

Comparison between regenerative-feedback and cofeedback gain-clamped EDFA

Abstract: The erbium-doped fiber amplifier (EDFA) with regenerative feedback is compared with the cofeedback scheme. Without the bandpass filter, the injected signal experiences regenerative amplification and results in a higher signal gain. Such an above-threshold regenerative amplifier also exhibits a lower noise figure due to a higher inversion for the transition corresponding to the signal wavelength of 1550 nm. A near quantum-limited noise figure of 3.1 dB is achieved at the maximum pump power of 134.5 mW, showing nearly complete inversion at the EDF input end in the regenerative-feedback scheme. A low (<10/sup -10/) bit-error rate has been achieved with saturation input signal power above -12 dBm.

Lasing wavelength dependence of gain-clamped EDFA performance with different optical feedback schemes

Abstract: Performance of gain-clamped erbium-doped fibre amplifier with different optical feedback schemes has been studied as a function of lasing wavelength. An inverse relation of the signal gains with the amplified spontaneous emission spectrum is observed for the entire laser tuning range as a result of the population variation caused by the different strength of the oscillating laser. The noise figure also shows a feature of the lasing wavelength dependence. However, co-feedback scheme exhibits behaviour opposite to that of the counter-feedback.

Uni- and bi-directional feedbacks regenerative EDFA operating below threshold

Abstract: In this paper, the performance of unidirectional and bi-directional regenerative erbium-doped fiber amplifier (EDFA) operating below laser oscillation threshold is compared. The experimental results show that the unidirectional system bas a higher gain and a lower noise figure than that of the bidirectional system. Resonant-amplification characteristic of regenerative amplifier is observed at low input signal for both schemes.

Unidirectional and Bidirectional Feedback Regenerative Erbium-Doped Fiber Amplifier : Instrumentation, Measurement, and Fabrication Technology

Abstract: In this letter, the performance of a unidirectional feedback regenerative erbium-doped fiber amplifier (EDFA) is compared with that of a bidirectional feedback one. The systems operate above the laser oscillation threshold, and exhibit the gain-clamping effect. The experimental results show that the unidirectional system has a higher gain and a lower noise figure than the bidirectional system. At high input signals, an injection-locking phenomenon is observed and the resonant-amplification characteristic of regenerative amplifier vanishes.

Saturation Characteristics of Regenerative Erbium-Doped Fiber Amplifier

Abstract: A regenerative erbium-doped fiber amplifier (EDFA) operating below oscillation threshold is presented. The saturation characteristics of the on-resonance and off-resonance are studied as a function of signal detuning. The dependence of amplification bandwidth on the input signal level is presented to show the saturation effects. It was found that the high gain performance of resonant amplification is preserved only for a small input signal. On-resonance signal gain as high as 35.1 dB has been achieved with a pump power as low as 29.4 mW. With different detuning parameters, saturated input signal powers were found to be asymmetric between positive and negative detuning. A low (< 10-10) bit-error-rate (BER) has been achieved with high input signal. The transmission performance was significantly deteriorated as the amplifier input power decreased.

Gain enhancement in L‐band EDFA using a fiber Bragg grating

Abstract: Gain enhancement in a long-wavelength band (L-band) erbium-doped fiber amplifier (EDFA) is demonstrated using a broadband fiber Bragg grating (BB FBG) that reflects the L-band amplified spontaneous emission (ASE) and L-band signal back into the system. The reflected L-band signal is then pumped by the unused conventional band (C-band) backward ASE, resulting in gain improvement. Gain enhancement as high as 11 dB is obtained for a 1560 nm signal, with an input power of −30 dBm at 98 mW of pump power. The noise figure for the wavelength is measured to be 4 dB. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 388–390, 2002.

Unidirectional and bidirectional feedback regenerative erbium-doped fiber amplifier

Abstract: In this letter, the performance of a unidirectional feedback regenerative erbium-doped fiber amplifier (EDFA) is compared with that of a bidirectional feedback one. The systems operate above the laser oscillation threshold, and exhibit the gain-clamping effect. The experimental results show that the unidirectional system has a higher gain and a lower noise figure than the bidirectional system. At high input signals, an injection-locking phenomenon is observed and the resonant-amplification characteristic of regenerative amplifier vanishes.

Gain and Noise Figure Improvements in Double Pass L-band EDFA using a Band-pass Filter

Abstract: A new double pass long wavelength band erbium-doped fiber amplifier (L-band EDFA) configuration with improved gain and noise figure is demonstrated by placing a band-pass filter in the output end of the erbium-doped fibre (EDF). Compared to the previous double pass amplifier, the proposed amplifier provides a maximum gain enhancement of 1.5 dB with reduction of noise figure by 1.2 dB at a pump power of 83 mW.

Double pass L-band EDFA incorporating band pass filter

Abstract: A new double pass long wavelength band erbium-doped fiber amplifier (L-band EDFA) system with improved gain and noise figure is demonstrated by incorporating a band-pass filter. Compared to the previous double pass amplifier, the proposed amplifier provides a maximum gain enhancement of 1.5 dB with reduction of noise figure by 1.2 dB at a pump power of 83 mW. The double pass system with BPF can give an equal value of gain as single pass system, but using only 62% of pump power.

Gain flattening and clamping in L-band ring EDFA incorporating fiber Bragg grating

Abstract: A new design of long wavelength band erbium-doped fiber amplifier (L-band EDFA) is experimentally demonstrated based on ring laser cavity to obtain better gain flatness as well as gain clamping characteristics. It uses a fibre Bragg grating (FBG) to provide laser feedback, which is arranged to propagate in the opposition to the signal in the amplifier by a pair of circulators. A flat-gain spectrum with less than 1.1 dB variation between 1568 nm and 1604 nm was observed with the laser wavelength at 1560 nm. A gain-clamping effect also was observed with this configuration, which provided a constant gain for all tested input signal powers from -40 dBm until 0 dBm.

Saturation Characteristics of Regenerative Erbium-Doped Fiber Amplifier : Optics and Quantum Electronics

Abstract: A regenerative erbium-doped fiber amplifier (EDFA) operating below oscillation threshold is presented. The saturation characteristics of the on-resonance and off-resonance are studied as a function of signal detuning. The dependence of amplification bandwidth on the input signal level is presented to show the saturation effects. It was found that the high gain performance of resonant amplification is preserved only for a small input signal. On-resonance signal gain as high as 35.1 dB has been achieved with a pump power as low as 29.4 mW. With different detuning parameters, saturated input signal powers were found to be asymmetric between positive and negative detuning. A low (< 10-10) bit-error-rate (BER) has been achieved with high input signal. The transmission performance was significantly deteriorated as the amplifier input power decreased.

Fabrication of Fiber Bragg Gratings in High Germania Boron Co-doped Optical Fiber by the Phase Mask Method

Abstract: Kaedah untuk menghasilkan peranti FBG yang mempunyai peratus pantulan yang tinggi diperkenalkan. Peranti FBG telah dicetak dalam gentian optik khas yang mengandungi germanium dan boron yang tinggi. Kandungan germanium ion di dalam gentian optik teras adalah sebanyak mol 20%. Cara yang digunakan ialah cara percetakan topeng fasa dengan menggunakan cahaya ultra ungu ion yang mempunyai panjang gelombang 244 nm sebagai sumber cahaya. Kami telah berjaya menghasilkan FBG yang mempunyai peratus pantulan setinggi 99.9% dan masa yang diambil untuk cetakan adalah kurang daripada 10 minit. Kata kunci: gentian optik; peranti FBG; laser UV; panjang gelombang Bragg; topeng fasa A technique to fabricate high reflectivity fiber Bragg gratings (FBGs) with minimal optics is presented. The FBG is written in high germania boron co-doped optical fiber using a phase mask with a 244 nm continuous-wave UV light as the printing source. The mol percentage of germania ion in the fiber core is about 20%. We have successfully fabricated FBGs with reflectivity as high as 99.9% in less than 10 minutes of exposure time. Key words: Optical fiber; fiber Bragg grating; UV laser; Bragg wavelength; phase mask

Highly Efficient L-Band Erbium-Doped Fiber Amplifier with Unpumped Erbium-Doped Fiber in Double Pass Configuration

Abstract: A double-pass long-wavelength-band erbium-doped fiber amplifier (L-band EDFA), which can effectively suppress and completely exploit the backward amplified spontaneous emission (ASE), is presented in this paper. Our experimental results have shown that, compared to a conventional single-pass amplifier, the gain coefficient can be improved considerably from 1.5 dB/mW to 3.1 dB/mW with only a small increase in the noise level. The L-band EDFA can also reduce the pump power necessary to achieve a specified gain to about half, at the cost of a noise figure increase of 1.6 dB. The maximum gain improvement of 15.5 dB was observed at a signal wavelength of 1572 nm of while signal and pump powers were fixed at -30 dBm and 103 mW, respectively.

Gain control in L-band erbium-doped fiber amplifier incorporating broadband fiber Bragg grating

Abstract: Gain control in a two-stage long-wavelength (L-band) erbium-doped fiber amplifier (EDFA) is demonstrated. Two circulators and a broadband fiber Bragg grating (FBG) are used to route a wasted backward conventional band (C-band) amplified spontaneous emission (ASE) from the second stage and launch it back into the input end of the first stage. The amplifier gain is clamped at 16.5 dB with variation less than 0.2 dB and the dynamic range up to -7.5 dBm for the VOA loss of 4 dB. The clamped gain level can also be controlled from 15.0 to 22.9 dB by increasing the VOA loss from 0 to 32 dB without significant variation in the noise figure.

Noise Characteristics of Erbium-Doped Fiber Amplifier with Optical Counter-Feedback

Abstract: Noise figure characteristics of erbium-doped fiber amplifiers (EDFAs) with different counter-feedbacks and without feedback are presented. The dependence of the depth of dip for the noise figure on the feedback type at moderately saturated input signal power was observed. Operating in the moderately saturated regime, the dip effect was found to be enhanced by introducing the optical counter-feedback. A noise figure near the quantum-limit has been achieved in this regime.

A study of laser SNR in an erbium-doped fiber laser subject to external injection

Abstract: Variation of laser signal-to-noise ratio (SNR) in an erbium-doped fiber-ring laser system subject to external injection is presented. Laser SNR is found to be dependent not only on the injected power, but also on the amplification characteristic over the entire amplified spontaneous emission (ASE) bandwidth. Both laser SNR and injected power as a function of the signal detuning show an inverse relation with the ASE spectral profile. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 40–42, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10509