Ravinder K. Jain

A broadly tunable wavelength-selectable WDM source using a fiber Sagnac loop filter

In this letter, we describe a new discretely wavelength-selectable 1.5-/spl mu/m source based on the use of a fiber Sagnac loop filter leading to the possibility of an efficient all-fiber source. The filter has an /spl sim/1.6-dB insertion loss, 14-dB peak-to-valley transmission ratios, and can be tuned to a very precise match with the International Telecommunications Union-wavelength-division-multiplexing grid. We demonstrate 25-channel outputs with precise 50-GHz channel spacings and very large (65 dB) output signal to background noise ratios.

Third-order optical nonlinearity in ZnO microcrystallite thin films

We report the measurement of third-order optical nonlinearity (χ(3)) of ZnO microcrystallite thin films near the excitonic resonance at various temperatures using the femtosecond degenerate four-wave-mixing technique. The measured χ(3) response times are 270, 240, and 160 fs at 4.2 K, 77 K, and room temperature, respectively. The values of χ(3) range from 10−7 to 10−4 esu. The maximum values of χ(3) always correspond to the absorption peaks at different temperatures. Room-temperature excitonic enhancement of χ(3) is also observed.

Precisely and rapidly wavelength-switchable narrow-linewidth 1.5-μm laser source for wavelength division multiplexing applications

We report the design and demonstration of a novel narrow-linewidth fiber laser that is switchable (at microsecond speeds) to precise predesignated wavelengths. This simple multiwavelength source, based on off-the-shelf components (fiber Bragg gratings (FBGs) and fiber Fabry-Perot filters), appears very promising for wavelength-division multiplexing.

Measuring intracavity phase changes by use of double pulses in a linear cavity

We report the use of a mode-locked linear-cavity Ti:sapphire laser as a sensitive phasemeter. We were able to generate two pulses in the cavity by placing an absorbing-dye jet in the middle of the cavity. A voltage applied to an intracavity LiNbO(3) crystal modified the phase velocity for one of the two pulses at each of its passes. We could then measure accurately the change in optical cavity length by observing a beat frequency between the two pulses. We measured the ratio of the r(33) to r(13) electro-optic coefficients in LiNbO(3) to be 3.57+/-0.1 , in close agreement with the accepted value of 3.62.

Electro-optic coefficients of lithium tantalate at near-infrared wavelengths

The unclamped linear electro-optic coefficients r13 and r33 for lithium tantalate are known at only one wavelength, 632.8 nm, whereas the clamped coefficients are also known at 3.39 μm. In the unclamped mode the effects of mechanical changes caused by piezoelectric and elasto-optic effects are accounted for in the electro-optic coefficient. We demonstrate a novel technique that uses a ferroelectric domain micropatterned electro-optic deflector to measure the unclamped linear electro-optic coefficients r13 and r33 at any wavelength. Using this method, we have determined these values for lithium tantalate at 980, 1330, and 1558 nm.

First demonstration of thermally poled electrooptically tunable fiber Bragg gratings

We demonstrate electrooptic tuning of a fiber Bragg grating (FBG) fabricated in a thermally poled fiber. 40 pm of tuning was demonstrated, corresponding to an electrooptic coefficient of 0.25 pm/V. Such electrooptic tunable FBGs have strong potential for numerous devices, including all-fiber amplitude modulators and high-speed tunable filters.

Bidirectional mode-locked fiber ring laser using self-regenerative, passively controlled, threshold gating

We demonstrate a technique to achieve bidirectional mode locking of a fiber ring laser using two amplitude modulators passively driven by a signal regenerated from the oscillation of the laser itself. The new scheme allows generation of two independent-frequency unlocked-countercirculating pulses and active control of their crossing points. The technique minimizes the effects of the dead band associated with crossing at a scattering media. Results show stable bidirectional pulses at a 5MHz repetition rate with no detectable dead band.

Near-IR tunable laser with an integrated LiTaO3 electro-optic deflector.

We report the successful demonstration of a near-IR tunable laser (1525.4-1558.2 nm) that uses an integrated LiTaO3 deflector in combination with a reflection grating as an electronically tunable filter. The electro-optic deflector is a unique integrated optical device and consists of a horn-shaped array of electro-optic prisms in series. The almost 33 nm of tuning covers a wavelength region of high interest to the communications industry (1527-1550 nm).

A compact diode-pumped passively Q-switched mid-IR fiber laser

A compact cladding-pumped Er:ZBLAN mid-infrared pulsed fiber laser using a liquefying gallium mirror as a saturable absorber is demonstrated for the first time. Preliminary results give pulse widths of 7 µs and energies of 38 nJ.

Picosecond pulse generation in CW semiconductor lasers using a novel regenerative gain-switching technique

The authors demonstrate a technique for regeneratively gain-switching semiconductor laser diodes to generate picosecond pulses with tunable repetition rates. The technique is applied to several semiconductor laser diodes, and pulse widths of the order of 35 ps and tuning of the repetition rate from approximately 200-500 MHz were obtained in preliminary experiments. With further refinements, such as the use of higher bandwidth diode lasers (including surface emitting lasers), special saturable absorbers (e.g. a dual segment laser with one segment biased below transparency) and broadband RF harmonic generators (including step recovery diodes, nonlinear transmission lines, and pulse forming networks), pulse widths as short as approximately 10 ps are anticipated.<<ETX>>