W-type and Graded-index bismuth-doped fibers for efficient lasers and amplifiers operating in E-band.

In this paper, we focus on the fabrication and investigation of optical properties of W-type and Graded-index single-mode Bi-doped germanosilicate fibers. The laser and gain characteristics of Bi-doped fibers of new designs were studied. It was shown that by variation of doping profile, it is possible to change characteristic parameters (active absorption, unsaturable loss level) of the active medium and, as a consequence, achieve an improvement of the performance of the optical devices based on these types of fibers. As a progress one can consider the creation of a Bi-doped fiber laser operating at 1460 nm with a record efficiency of 72% using a relatively short active fiber (L = 75 m); and a 20-dB Bi-doped fiber amplifier (L = 120 m) with a pump power of 45 mW (for the input signal powers lower than 30 µW) having a high gain efficiency of 0.52 dB/mW. We suggest that the obtained results could be a driver for further investigation in this direction.

40 dB gain all fiber bismuth-doped amplifier operating in the O-band.

In this Letter, we investigate and compare the gain and noise figure characteristics of bismuth (Bi)-doped fiber amplifiers configured in both single and double signal pass implementations. A maximum gain of 25 dB and a noise figure of 4 dB is measured at 1360 nm in the single pass configuration for -23 dBm input signal power, whereas in the double pass configuration the gain of the amplifier is improved significantly by 14 dB allowing us to achieve a gain of 39 dB with a noise figure of 5 dB. To the best of our knowledge, this is the highest gain reported to date using Bi-doped fiber as a gain medium. Furthermore, we also study the gain and noise figure dependency on pump power, signal power, and pump wavelength for the double pass amplifier configuration. We observed similar gain and noise figure performance in the double pass configuration to that of the single pass configuration but with the benefit of less pump power and a shorter length of the Bi-doped fiber.

Highly efficient thulium-doped high-power laser fibers fabricated by MCVD.

We report a hybrid process by combining both vapor-phase and solution-doping techniques of rare-earth doped preform fabrication in conjunction with the MCVD technique, in order to fabricate highly efficient Tm-doped laser fibers. The proposed fabrication route takes advantage of co-doping silica with high alumina content through the vapor-phase doping process, which is otherwise difficult to achieve using conventional solution doping technique. In addition, by employing the solution doping method, high-purity thulium halide precursors that have low vapor pressures up to several hundred degree Celsius. These high-purity thulium halide precursors can be used to dope the fiber core region with a high thulium concentration that is optimized for an efficient two-for-one cross-relaxation process for 79xnm diode pumped thulium-doped fiber laser. Fibers fabricated using the hybrid approach show more homogeneous and flat-top dopant profiles, compared with the conventional approach, where both aluminum and thulium are incorporated in the core through solution doping. This will ensure that more doped region will take part in the cross-relaxation process. Superior laser performance with a slope efficiency of >70% in the two-micron band has been demonstrated when diode pumped at ~790nm.

Bismuth-doped all-fiber mode-locked laser operating at 1340 nm.

We demonstrate a 1340 nm mode-locked Bismuth (Bi)-doped fiber laser without any saturable absorber. The effect of pump power on pulse width is studied, and a variation from 1.5 to 3 ns is reported. The output of the mode-locked Bi-doped fiber laser is further amplified using a master oscillator power amplifier configuration, and a peak power of 1.15 W is achieved. Soliton bunching is observed, and a true pulse width of 1.2 ps is reported from the measured autocorrelation trace. Stable operation of the mode-locked laser is verified from the radio-frequency spectrum with a fundamental repetition rate of 6.3 MHz, and SNR of 65 dB.

Bi-doped fiber amplifier with a flat gain of 25 dB operating in the wavelength band 1320-1360 nm.

Bismuth (Bi)-doped phosphosilicate fibers have been fabricated by the modified chemical vapor deposition (MCVD)-solution doping technique under different process conditions. The influence of fabrication conditions on unsaturable loss in fibers has been investigated. Pump wavelength dependent Bi gain has been studied to obtain a flat gain over a wide bandwidth. A diode pumped all-fiber Bi-doped amplifier with a flat gain of 25±1 dB from 1320-1360 nm (40 nm) has been demonstrated for -10 dBm of input signal power with a noise figure (NF) ranging from 4-6 dB. Moreover, a small signal gain of 29 dB and a NF of 4.5 dB at 1340 nm has been achieved for an input signal power of -30 dBm.

1120 nm diode-pumped Bi-doped fiber amplifier.

Bismuth-doped aluminosilicate fiber has been fabricated by the MCVD-solution doping method and characterized for its unsaturable loss and gain. The amplifier performance has been compared for a novel pumping wavelength of 1120 nm with the conventional pumping wavelength region of 1047 nm. Unsaturable loss was 65% and 35% at 1047 and 1120 nm, pump wavelengths, respectively. A maximum gain of about 8 dB at 1180 nm for a fiber length of 100 m was observed with 1120 nm pumping. Gain enhancement of 70% was achieved with the 1120 nm pump as compared to the 1047 nm pump. A further 3.5 dB gain was obtained on simultaneous pumping at 1047 and 1120 nm.

Excited-state absorption in various bismuth-doped fibers.

Excited-state absorption (ESA) in various bismuth-doped fibers (BDFs) was investigated. No significant ESA in IR emission bands of Bi-doped germanosilicate and phosphosilicate fibers was found. Considerable ESA was observed in Bi-doped aluminosilicate fibers at 800-1700 nm. The ESA spectra of the aluminosilicate BDFs with different bismuth concentration were measured at room and 77 K temperature. Significant dependence of the ESA on the bismuth concentration and the fiber temperature was found.

Optical amplification in 1430-1495 nm range and laser action in Bi-doped fibers.

An emission band with a maximum at 1430 nm and a FWHM of 100 nm was observed in a Bi-doped fiber under core-pumping in the 1340- 1370 nm wavelength range. Net gain in 1430-1490 nm and laser action in 1443-1459 nm wavelength range in the Bi-doped aluminosilicate fiber have been demonstrated for the first time to our knowledge.

Bismuth-doped-glass optical fibers--a new active medium for lasers and amplifiers.

Optical fibers with bismuth-doped silicate and germanate glass cores were fabricated by the modified chemical vapor deposition technique (solution and vapor-phase Bi incorporation). The fibers revealed an efficient luminescence with a maximum in the 1050-1200 nm spectral range, FWHM up to 200 nm, and a lifetime of the order of 1 ms.