http://www-personal.umich.edu/~andrewcb/DSO/Papers/compact%20grating-stabilized%20diode%20laser%20system%20for%20atomic%20physics.pdf

A compact grating-stabilized diode laser system for atomic physics

A communications network has a plurality of nodes interconnected by an optical transmission medium. The transmission medium is capable of a carrying a plurality of wavelengths organized into bands. A filter at each node for drops a band associated therewith and passively forwards other bands through the transmission medium. A device is provided at each node for adding a band to the transmission medium. Communication can be established directly between a pair of nodes in the network sharing a common band without the active intervention of any intervening node. This allows the network to be protocol independent. Also, the low losses incurred by the passive filters permit relatively long path lengths without optical amplification.

WDM optical network with passive pass-through at each node

We review recent breakthroughs in the silicon photonic technology and components, and describe progress in silicon photonic integrated circuits. Heterogeneous silicon photonics has recently demonstrated performance that significantly outperforms native III/V components. The impact active silicon photonic integrated circuits could have on interconnects, telecommunications, sensors, and silicon electronics is reviewed.

Heterogeneous Silicon Photonic Integrated Circuits

Experimental and theoretical investigations of coherent optical-frequency-domain reflectometry using semiconductor laser sources are presented. Good agreement was found between the analysis of the signal-to-noise ratio due to the phase noise and the experimental results. The sensitivity limit due to the quantum noise is also described. Limitations due to the nonlinearity in the optical frequency sweep produced by the thermal-response time of the laser and mode hopping are investigated and compared with experimental results. Two interferometric methods to characterize the thermal-response time of the laser and their implementations are described. The effects of mode hopping in the optical-frequency sweep are compared to numerical simulations. A simple formula to predict the position of spurious peaks due to mode hopping are presented. A spatial resolution of 400 /spl mu/m over 10 cm was obtained by correcting the nonlinearity in the optical-frequency sweep by using an auxiliary interferometer. The Rayleigh backscattering was observed for the first time over more than 400 m of fiber using a DFB laser coupled to an external cavity. >

Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources

A new technique of cavity enhanced absorption spectroscopy is described. Molecular absorption spectra are obtained by recording the transmission maxima of the successive TEMoo resonances of a high-finesse optical cavity when a Distributed Feedback Diode Laser is tuned across them. A noisy cavity output is usually observed in such a measurement since the resonances are spectrally narrower than the laser. We show that a folded (V-shaped) cavity can be used to obtain selective optical feedback from the intracavity field which builds up at resonance. This induces laser linewidth reduction and frequency locking. The linewidth narrowing eliminates the noisy cavity output, and allows measuring the maximum mode transmissions accurately. The frequency locking permits the laser to scan stepwise through the successive cavity modes. Frequency tuning is thus tightly optimized for cavity mode injection. Our setup for this technique of Optical-Feedback Cavity-Enhanced Absorption Spectroscopy (OF-CEAS) includes a 50 cm folded cavity with finesse ∼20 000 (ringdown time ∼20 μs) and allows recording spectra of up to 200 cavity modes (2 cm−1) using 100 ms laser scans. We obtain a noise equivalent absorption coefficient of ∼5×10−10 cm−1 for 1 s averaging over scans, with a dynamic range of four orders of magnitude.

Fast, low-noise, mode-by-mode, cavity-enhanced absorption spectroscopy by diode-laser self-locking

We present a theory of adiabatic chirp reduction and narrowing of the Lorentzian laser line that occurs when a laser is coupled to an external passive resonator. Chirp reduction and line narrowing are simply related. We show that the reduction in the Lorentzian line width is equal to the square of the reduction in adiabatic chirp. Both are strongly enhanced near resonances of the external cavity.

The relation of line narrowing and chirp reduction resulting from the coupling of a semiconductor laser to passive resonator

An optical communication network includes a novel, passive optical component. This component combines the function of a splitter with the function of a wavelength-division multiplexer. These functions are performed in distinct wavelength bands. In one embodiment, the inventive component is made using silicon optical bench technology.

Optical network comprising a compact wavelength-dividing component

An optical device is disclosed which provides wavelength multiplexing/demultiplexing utilizing a plurality of focusing Bragg reflectors (14,18,22,26). Each Bragg reflector includes a plurality of confocal (i.e., common foci) elliptical grating lines, with the exit/entrance ports of the input/output waveguides (12,16,20,24,28) located at the foci of the ellipse. By virtue of the elliptical design, the signal propagating outward from the exit port of the input waveguide (12) will be reflected by the appropriate Bragg reflector and focused into the entrance port of the appropriate output waveguide (16,20,24,28). When each Bragg reflector exhibits a different ellipticity, but shares one common focal point, optical multiplexing/demultiplexing may be achieved. Optical filtering may be achieved when all Bragg reflectors are designed to have common foci.

Optical multiplexer/demultiplexer using focusing Bragg reflectors

Disclosed are planar waveguides comprising substantially polarization-independent Bragg gratings. A preferred embodiment of the invention comprises a Si body with a silica lower cladding layer thereon, and a phosphorus P-doped silica core on the lower cladding. Appropriate periodic recessed features are etched into the core, and phophorus P- and B-doped silica upper cladding is deposited over the core. The dopant concentrations are adjusted such that the refractive index difference between core and upper cladding is small (0.35-1.45×10-2), and such that the flow temperature of the upper cladding material is lower than that of the core material. In another preferred embodiment a thin layer of Si3 Nx (x˜4) is conformally deposited over the core after the grating etch, and the upper cladding material is deposited onto the Si3 Nx layer. Bragg devices according to the invention are advantageously used in Integrated Optical Circuits (IOCs), e.g. in IOCs used in WDM optical communication systems.

Optical waveguide comprising Bragg grating coupling means

We propose a new way of making highly resonant integrated optical circuits based on weak side-by-side coupling between waveguides and high Q distributed Bragg resonators. This method can be used to design a resonant optical reflector which, when used as a feedback element to a laser, will result in a compact structure that has both extremely narrow line width and very low chirp. By coupling the resonator to two waveguides, one on either side, an optical analog of the resonant transformer can be made. This device can be used for wavelength division multiplexing. Such multiplexer elements will both resonantly transform optical power from the laser to a common output channel and also provide feedback which locks the laser to the channel wavelength.

Charles Howard Henry

Papers

The relation of line narrowing and chirp reduction resulting from the coupling of a semiconductor laser to passive resonator

Optical network comprising a compact wavelength-dividing component

Optical multiplexer/demultiplexer using focusing Bragg reflectors

Optical waveguide comprising Bragg grating coupling means

Narrow-band resonant optical reflectors and resonant optical transformers for laser stabilization and wavelength division multiplexing