P. Poopalan

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

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.

Long-wavelength EDFA gain enhancement through 1550 nm band signal injection

Abstract An experiment on gain enhancement in the long band (L-band) is demonstrated. Gain at the L-band is relatively inefficient because the operating wavelengths are far from the peak emission band of erbium ions. Gain enhancement for the L-band is achieved by using a signal from the conventional band (C-band). The efficiency of gain enhancement is strongly determined by the absorption coefficient of the C-band signal. Gain enhancement as high as 5.3 dB is obtained at −15 dBm of 1535 nm injected signal. Maximum gain enhancement for other injected signal wavelengths can be optimised by varying their power. Noise figure penalty is measured to be less than 1.0 dB at its optimised power. Furthermore, there is no penalty on the noise figure for injected signals longer than 1545 nm.

Double-pass L-band EDFA with enhanced noise figure characteristics

A new double-pass long wavelength band erbium-doped fiber amplifier with enhanced noise figure characteristics is demonstrated by adding a short length of forward pumped erbium-doped fiber (EDF) in front of a double-pass amplifier. Compared with the conventional double-pass amplifier, the new amplifier provides noise figure improvement of about 0.8 to 6.0 dB over the flat-gain region from 1568 to 1600 nm. Since the optical circulator prevents the amplified signal and backward amplified spontaneous emission from propagating into the EDF, the population inversion of the input part of the amplifier is hardly affected by the intense lights, therefore, the noise figure could be kept low. The new double-pass system has achieved a flat-gain output at about 33.5 dB, which is 13.5 dB higher than that of the single-pass system with gain variation less than 1.3 dB at the flat-gain region. The noise figure varies from 5.9 to 6.6 dB in this region.

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

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.

All-optical gain-clamped erbium-doped fiber-ring lasing amplifier with laser filtering technique

A unique laser filtering technique of a gain-clamped erbium-doped fiber amplifier based on ring-laser cavity is demonstrated. The filtering mechanism is achieved using a single fiber Bragg-grating, which also functions as a laser feedback reflector at the output end of the amplifier. This new design has low noise and most important, shows up to 98% reduction in output laser intensity as compared with a previous design studied earlier. An optimum result with gain and noise around 25 and 3.5 dB, respectively, obtained for a dynamic range of input signal power up to -8 dBm.

High Sensitivity Fiber Bragg Grating Pressure Sensor Using Thin Metal Diaphragm

A high sensitivity pressure sensor design without a polymer transducer is demonstrated in this paper. The sensor uses a thin metal diaphragm as a pressure transducer instead of a polymer. The sensor is tested to a maximum pressure of 100 psi and has a sensitivity of 0.0115 nm/psi, which matches the calculated sensitivity of 0.0127 nm/psi. The sensor is provides accurate measurement of the pressure and shows good repeatability in its readings. The sensor is also tested at the flow loop of the University of Tulsa, and shows a good match with the pressure readings of the flow loop.

Gain clamping in two-stage L-band EDFA using a broadband FBG

A gain-clamped long wavelength band erbium-doped fiber amplifier (L-band EDFA) with an improved gain characteristic is demonstrated by simply adding a broadband conventional band (C-band) fiber Bragg grating (FBG) in a two-stage amplifier system. The FBG reflects backward C-band amplified spontaneous emission (ASE) from the second stage back into the system to clamp the gain. The gain is clamped at about 22.4 dB with a gain variation below 0.4 dB for input signal powers of -40 to -15 dBm. Compared with an unclamped amplifier of similar noise figure values, the small signal gain has improved by 2.4 dB due to the FBG which blocks the backward propagating ASE. At wavelengths from 1570 to 1600 nm, gain of the clamped amplifier varies from 19.4 to 26.7 dB. The corresponding noise figure varies by /spl plusmn/0.35 dB around 5 dB, which is not much different compared to that of the unclamped amplifier.

High-gain bidirectional Er/sup 3+/-doped fiber amplifier for conventional- and long-wavelength bands

High average gains of greater than 31 dB have been obtained between 1530-1560 nm (conventional-wavelength band, C-band) and 1570-1600 nm (long-wavelength band, L-band) using a saturating tone technique that represents 64 channels of a wavelength division multiplexed system. A bidirectional amplifying stage is utilized as high-power C-band and low-noise L-band stages. Noise figures of less than 3.6 and 5.4 dB are measured for the C- and L-bands, respectively.

Design optimisation of erbium-doped fibre ring laser through numerical simulation

Erbium-doped fibre ring laser is modelled, incorporating the effects of ion pairs, using the propagation and rate equations of a homogeneous, two-level medium. The numerical model has been obtained by developing a spectral analysis of erbium-doped fibre amplifiers. This approach is modified to account for the cyclical propagation of the field in the ring laser. Numerical simulations provide interesting information on the spectral behaviour as well as important parameters for device analysis and design, mainly the lasing wavelength and output power.

AC Conductivity and Dielectric Relaxation Behavior of Sol-gel BaxSr1-xTiO3 Thin Films

BaxSr1-xTi03 sol-gel thin films with x=0.5, 0.7 and 0.8 have been fabricated as AI/BST/Pt capacitor. The AC conductivity and dielectric properties over a frequency rang of 10 Hz and 1 MHz have been studied in order to explore the ion dynamics and relaxation mechanisms in the films. The frequency dependent conductivity plots show three regions of conduction processes. Dielectric results show that ɛ′ at low frequencies increases as Sr content decreases, whereas at high frequencies, it shows opposite variation, which is attributed to the dipole dynamics. The electric modulus plots reveal the relaxation peaks which are not observed in the ɛ″ plots and the contribution of the grains, grain boundaries and electrode to the relaxation mechanisms.