Fine Wavelength Tuning Research Articles

Size and emission wavelength control of InAs∕InP quantum wires

For a certain heteroepitaxial system, the optical properties of self-assembled nanostructures basically depend on their size. In this work, we have studied different ways to modify the height of InAs∕InP quantum wires (QWrs) in order to change the photoluminescence emission wavelength. One procedure consists of changing the QWr size by varying the amount of InAs deposited. The other two methods explored rely on the control of As∕P exchange process, in one case during growth of InAs on InP for QWr formation and in the other case during growth of InP on InAs for QWr capping. The combination of the three approaches provides a fine tuning of QWr emission wavelength between 1.2 and 1.9μm at room temperature.

External-cavity tunable mid-infrared laser using off-band surface-emitting Bragg grating coupler

An external-cavity laser using an integrated two-segment design allows broad and continuous wavelength tuning with independent control of power and wavelength. The laser has a gain segment and a surface-emitting Bragg grating segment that was designed to be off-band for zero reflection inside the cavity, and with a strong free-space coupling to an external mirror to form a linear cavity. Wavelength control was achieved with a combination of coarse and broad wavelength tuning (140nm) with the external mirror, and continuous, fine wavelength tuning via current-induced phase shift in the Bragg grating. Separate controls of the two segments allowed wavelength fine tuning without power variation and vice versa. The concept was applied to a 7μm laser, and is applicable to other wavelength.

Observation of acetylene molecular absorption line with tunable, single-frequency, and mode-hop-free erbium-doped fiber ring laser

We succeeded in observing one of the absorption lines of acetylene [P(16)] using an erbium-doped fiber-ring laser, which is the first such observation using a fiber-ring laser. The observed linewidth of the P(16) linear absorption was approximately 450 MHz. Mode competition and mode hopping were suppressed by using an ultra narrow-band fiber Bragg grating and a Fabry-Perot filter in the ring laser, respectively. Wavelength fine-tuning was carried out by changing the cavity length of the fiber-ring laser; the fine-tuning range was about 850 MHz (0.01 nm). Furthermore, wavelength tuning was achieved by controlling the temperature of the fiber Bragg grating, and the coarse timing range was about 0.2 mn.

Two-Photon Photoemission Spectroscopy of Adsorbed Molecules and Semiconductors.

Two-photon photoemission spectroscopy (2 PPES) has been applied to benzene adsorbed Cu(111) surface and to Si(001) surface. 2 PPES for benzene adsorbed Cu(111) surface has revealed the adsorption induced bonding and antibonding states and the image state. Resonance width between the bonding state and the image state is found to be very narrow, about 0.1 eV full width at half maximum. Sharp resonant photoexcitaion has also been found for Si(001) bulk bands. These results demonstrate the capability of 2 PPES in determining pairs of occupied and unoccupied states. Importance of fine wavelength tuning in 2 PPES is emphasized.

A Miniaturized Tunable Filter Based on a Fiber Bragg Grating Loaded by a Ceramic-Tube Microheater

A miniaturized 1.55 μm tunable fiber Bragg grating (FGB) filter is proposed and successfully demonstrated using an aluminum ceramic-tube with a tungsten thick film sleeve microheater. Fine tuning of the Bragg reflective wavelength with 0.0135 nm/oC is achieved by adding the constant thermal distribution along the uniform FBG with a 0.3 nm bandwidth. Furthermore, a 1.5 nm linearly chirped reflection bandwidth is obtained by thermal gradient loading.

Single lithium niobate crystal for mode selection and phase modulation in a tunable extended-cavity laser diode

A 1540-nm external-cavity laser diode with an intracavity electro-optic wavelength tuner is demonstrated. Coarse- and fine-wavelength tuning is achieved with a single lithium niobate wavelength tuner. One section of the crystal is used as a tunable-wavelength filter to tune the wavelength by mode hopping. The other operates as a phase modulator to change the optical length of the cavity and to tune the wavelength continuously. Coarse tuning by mode hopping is obtained over a range of 5.3 nm with a tuning rate of 580 MHz/V. Continuous tuning is obtained over 82% of the free spectral range of the cavity. The wavelength switching time is 10 ns for the cavity used.

Temperature tuned distributed feedback dye laser with high repetition rate

A pulsed subnanosecond laser system is described which is tunable over the spectral range from 450 to 650 nm with a bandwidth of ~0.006 nm and can be operated with a repetition rate of up to 200 Hz. It consists of a mirror tuned distributed feedback dye laser which is directly pumped by a XeCl excimer laser. Fine tuning and accurate stabilization of the dye laser wavelength are performed by electronically controlling the temperature of the dye liquid. The long-time stability of the laser wavelength is 0.0028 nm; this is achieved by a novel mechanical and electronic arrangement.

Studies of stacking-fault contrast by synchrotron X-ray section topography

The periodicities, profiles and contrast of stacking-fault fringes observed in high-resolution synchrotron X-ray section topographs have been comprehensively studied with controlled changes of diffraction parameters such as wavelength and polarization mode, which allowed observations under diffraction conditions inaccessible with conventional sources of characteristic radiation. Comparisons with simulated patterns and computed fringe profiles are presented. The fringe patterns were generated by a single intrinsic stacking fault of area 1.3 mm2 contained in a polished parallelepiped specimen of natural diamond unusually free from lattice defects producing long-range strains. The principal X-ray wavelengths employed were 0.08, 0.10, 0.12 and 0.15 nm, providing values of μ0t0 ranging from 0.25 to 1.5 (μ0 = normal photoelectric absorption coefficient, t0 = specimen thickness). Fringe orders up to about 100 were observed at the longer wavelengths. Controlled fractional changes of Pendellosung interference order were obtained by wavelength fine-tuning (Δλ ≃ 10−3 nm). Matching of simulations with the resultant patterns is discussed in detail. Fringe patterns were recorded with pure σ, pure π and mixed polarization modes. Change of polarization mode was employed in order to vary the ratio of anomalous to normal absorption without having to change other diffraction variables. Particular attention was devoted to exploring the range of diffraction conditions under which fault vector sign could be experimentally determined from the sign of `first-fringe' contrast, and to examining how this range can be extended with the aid of comparison with pattern simulations.