Uh-Chan Ryu

Enhancement of power conversion efficiency for an L-band EDFA with a secondary pumping effect in the unpumped EDF section

A novel structure, which utilizes detrimental backward amplified spontaneous emission as a secondary pump source is suggested for a silica-based fiber amplifier, operating at a wavelength range from 1570 to 1610 nm. By using the secondary pumping effect from the strong, wasted 1550-nm band amplified spontaneous emission power in the unpumped section of the erbium-doped fiber, it was possible to achieve a considerable improvement in power conversion efficiency, increasing small-signal gain by more than 4 dB. The suggested pump structure was also shown to be useful in overall conversion efficiency improvement for L-band EDFAs, regardless of pump wavelength choice.

Compensation of Raman-induced crosstalk using a lumped germanosilicate fiber Raman amplifier in the 1.571-1.591-μm region

A new method to equalize power imbalance caused by Raman-induced crosstalk among optical channels is proposed using a lumped germanosilicate fiber Raman amplifier. Evolution of optical channels through the Raman amplifier was simulated using Raman frequency modeling, which theoretically predicted simultaneous amplification and power equalization. Experimentally, a gain band with negative slope in the range of 1.571-1.591 /spl mu/m was achieved in a lumped Raman amplifier pumped by a broad-band laser diode centered at 1.467 /spl mu/m. We demonstrated compensation of the Raman-induced crosstalk of 5 dB accumulated along 330 km of conventional single-mode fiber.

Inherent enhancement of gain flatness and achievement of broad gain bandwidth in erbium-doped silica fiber amplifiers

We report new methods to inherently increase the flatness and bandwidth of erbium-doped silica fiber amplifiers from three perspectives: fiber design, pump-signal WDM coupler optimization, and amplifier structure. First, to achieve inherent control of the gain spectrum, a new type of composite fiber structure with an Er-doped core and a Sm-doped cladding ring is proposed and experimentally demonstrated. Interaction of the optical field with the Sm-doped cladding to produce evanescent wave filtering is modeled, which provides an in-line control of gain fluctuation in the erbium-doped flier amplifier (EDFA) C band, 1530-1560 nm. Second, the effect of the spectral characteristics of WDM couplers over the L band of an EDFA is explored. A fused taper fiber coupler for a 1480-nm pump is optimized for signals in the wavelength range of 1570-1610 nm by measuring the small-signal gain, gain tilt, and noise figure in an L-band EDFA. Finally, a new all-fiber structure for a wide-band EDFA, where the L and C bands were coupled serially, is demonstrated with optimized pump-signal couplers. Further optimization of the new composite fiber structure and the transient effects in the serially coupled EDFAs are also discussed.

41-nm 3-dB gain-band optical amplifier using an Er-doped core and Sm-doped inner-cladding fiber without external filters

A new fiber structure optical fiber amplifier was reported where the core was doped with erbium (Er) and the inner-cladding was doped with samarium (Sm). Feasibility of gain control by evanescent wave interaction with an absorbing material in the inner-cladding was experimentally demonstrated. The optical amplifier using the proposed fiber resulted in the gain variation between gain peak and valley less than 2.5 dB without using external gain equalizing filters.

In-line gain control of the erbium doped fiber amplifier using samarium doped inner-cladding in the 1.5 /spl mu/m region

A new type of erbium doped fiber for optical amplifier was reported where erbium was doped in the center of the core and samarium doped in a ring in the cladding. By utilizing the spectral overlap of the absorption cross section of samarium in the inner-cladding and the emission cross section of erbium ion in the core, we demonstrated a new way of in-line control the gain spectrum of erbium doped amplifier pumped at 980 nm. The gain spectra in the conventional band were measured and we demonstrated potential of gain-flattening in the 1.5 mm region without external filters using the specially designed fiber. The effects of samarium doped inner-cladding on amplified spontaneous emission in the long band were also reported.

Single Passband, Discretely Tunable, Photonic Microwave Bandpass Filter Based on Highly Birefringent Fiber-Based Comb Filter

By experiment, we demonstrate a photonic microwave finite impulse response (FIR) filter scheme that exhibits both the features of flexible frequency tuning and single passband. The proposed filter is constructed by the combined use of a broadband Gaussian-shaped supercontinuum (SC) and a wavelength spacing tunable, highly birefringent (Hi-Bi) fiber-based comb filter. By incorporating a three-segment, Hi-Bi fiber-based, Lyot-type, comb filter into a spectrum slicing-based photonic microwave FIR filter scheme, we achieve both novel features of single passband and passband RF frequency tuning at the same time. It is shown that the discrete tuning of passband RF frequency can be obtained simply by rotating beam polarization. Our experimental demonstration shows a flexible passband RF frequency tuning over a range of 7.3 GHz.

Athermal optical gain block in C-band by serial concatenations of erbium-doped antimony oxide silica glass fiber

We report a new novel technique to suppress the temperature-dependent gain (TDG) of erbium-doped fiber amplifier in the C-band by providing a composite optical gain block, conventional erbium-doped fiber (EDF) serially concatenated with Sb-doped silica EDF. Compared with conventional EDFs, Sb-doped silica EDF showed an opposite TDG coefficient in the C-band. Detailed experimental athermalization schemes are reported for various concatenating configurations. The temperature-dependent optical gain variation was suppressed within /spl plusmn/0.35 dB for the temperature range of -40/spl deg/C to +80/spl deg/C from 1530 to 1560 nm.

Emission Cross-Section Synthesis in Rare Earth Doped Optical Fiber

Novel techniques to control the effective emission cross-section of a rare-earth doped fiber with functional cladding structures are reviewed. Evanescent wave filtering with absorbing inner clad ring and W-type three layered fiber structure are discussed.

Suppression of temperature dependence in EDFA gain by hybrid concatenation of antimony-doped silica EDF

Sb-doped silica EDF showed an opposite temperature dependent gain coefficients compared to Al-doped silica EDFs. Concatenation of two EDFs resulted in a gain variation less than /spl plusmn/0.25 dB for the saturated gain over 15 dB, within -40 to +80 /spl deg/C.

Gain Controlling of Erbium-Doped Fiber Amplifier by Samarium Doped Inner-Cladding in the 1.5µm Region

Characteristics of a new type of erbium-doped fiber for optical amplifiers were reported where erbium was doped in the center of the core and samarium doped in a ring of the cladding. Using samarium absorption of photons around 1.5 μm in the erbium ion emission range, we demonstrated a new way of controlling the gain spectrum of erbium-doped fiber amplifier without using external filters. Amplifier small signal gain under saturation was about 11 dB and within 2.3 dB variation in the range of 1520-1560 nm. Total output power from the amplifier was 9dBm with 100 mW of pump power at 980 nm. The effects of samarium-doped inner cladding on amplified spontaneous emission spectra in the long wavelength band were also reported.Characteristics of a new type of erbium-doped Wber for optical ampliWers were reported where erbium was doped in the center of the core and samarium doped in a ring of the cladding. Using samarium absorption of photons around 1.5 ·m in the erbium ion emission range, we demonstrated a new way of controlling the gain spectrum of erbium-doped Wber ampliWer without using external Wlters. AmpliWer small signal gain under saturation was about 11 dB and within 2.3 dB variation in the range of 1520± 1560 nm. Total output power from the ampliWer was 9 dBm with 100 mW of pump power at 980 nm. The eVects of samarium-doped inner cladding on ampliWed spontaneous emission spectra in the long wavelength band were also reported.