We review the field of femtosecond pulse shaping, in which Fourier synthesis methods are used to generate nearly arbitrarily shaped ultrafast optical wave forms according to user specification. An emphasis is placed on programmable pulse shaping methods based on the use of spatial light modulators. After outlining the fundamental principles of pulse shaping, we then present a detailed discussion of pulse shaping using several different types of spatial light modulators. Finally, new research directions in pulse shaping, and applications of pulse shaping to optical communications, biomedical optical imaging, high power laser amplifiers, quantum control, and laser-electron beam interactions are reviewed.

Femtosecond pulse shaping using spatial light modulators

The various arguments for introducing optical interconnections to silicon CMOS chips are summarized, and the challenges for optical, optoelectronic, and integration technologies are discussed. Optics could solve many physical problems of interconnects, including precise clock distribution, system synchronization (allowing larger synchronous zones, both on-chip and between chips), bandwidth and density of long interconnections, and reduction of power dissipation. Optics may relieve a broad range of design problems, such as crosstalk, voltage isolation, wave reflection, impedence matching, and pin inductance. It may allow continued scaling of existing architectures and enable novel highly interconnected or high-bandwidth architectures. No physical breakthrough is required to implement dense optical interconnects to silicon chips, though substantial technological work remains. Cost is a significant barrier to practical introduction, though revolutionary approaches exist that might achieve economies of scale. An Appendix analyzes scaling of on-chop global electrical interconnects, including line inductance and the skin effect, both of which impose significant additional constraints on future interconnects.

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Rationale and challenges for optical interconnects to electronic chips

Femtosecond optical pulse shaping and processing

Apparatus and method for increasing the sensitivity in the detection of optical coherence tomography and low coherence interferometry (“LCI”) signals by detecting a parallel set of spectral bands, each band being a unique combination of optical frequencies. The LCI broad bandwidth source is split into N spectral bands. The N spectral bands are individually detected and processed to provide an increase in the signal-to-noise ratio by a factor of N. Each spectral band is detected by a separate photo detector and amplified. For each spectral band the signal is band pass filtered around the signal band by analog electronics and digitized, or, alternatively, the signal may be digitized and band pass filtered in software. As a consequence, the shot noise contribution to the signal is reduced by a factor equal to the number of spectral bands. The signal remains the same. The reduction of the shot noise increases the dynamic range and sensitivity of the system.

Apparatus and method for ranging and noise reduction of low coherence interferometry LCI and optical coherence tomography OCT signals by parallel detection of spectral bands

An apparatus and method are provided. In particular, at least one first electro-magnetic radiation may be provided to a sample and at least one second electro-magnetic radiation can be provided to a non-reflective reference. A frequency of the first and/or second radiations varies over time. An interference is detected between at least one third radiation associated with the first radiation and at least one fourth radiation associated with the second radiation. Alternatively, the first electro-magnetic radiation and/or second electro-magnetic radiation have a spectrum which changes over time. The spectrum may contain multiple frequencies at a particular time. In addition, it is possible to detect the interference signal between the third radiation and the fourth radiation in a first polarization state. Further, it may be preferable to detect a further interference signal between the third and fourth radiations in a second polarization state which is different from the first polarization state. The first and/or second electro-magnetic radiations may have a spectrum whose mean frequency changes substantially continuously over time at a tuning speed that is greater than 100 Tera Hertz per millisecond.

Method and apparatus for performing optical imaging using frequency-domain interferometry

Several ultrafast optical pulse generation techniques utilizing external cavity semiconductor lasers are described. These techniques include active mode locking, passive mode locking, hybrid mode locking, and several chirp compensation techniques. Utilizing these techniques, optical pulses of 200 fs in duration with over 160 W of peak power have been generated, making these pulses both the shortest and most intense ever generated with a semiconductor injection diode laser system. These pulses have been used to study the ultrafast amplification characteristics of semiconductor lasers. The results presented reveal the nature of the effects which dominate the pulse shaping mechanisms in external cavity hybrid mode-locked diode lasers. >

High-power ultrafast laser diodes

A single-stripe GaAs-AlGaAs semiconductor optical amplifier (SOA) has been used to generate four tunable wavelength-division multiplexed (WDM) channels simultaneously, each transmitting 12-ps pulses at 2.5 GHz, for an aggregate pulse rate of 10 GHz. Wavelength tuning over 18 nm has been demonstrated with channel spacing ranging from 0.8 to 2.1 nm. A potential spectral correlation across the multiwavelength spectrum has been studied in both experiment and simulation methods. These results show the potential for utilizing single stripe laser diodes as multiwavelength sources in WDM-TDM network.

Multiwavelength 10-GHz picosecond pulse generation from a single-stripe semiconductor diode laser

Wideband spectral phase correlation is demonstrated from a multiwavelength mode-locked semiconductor laser. By use of frequency-resolved optical gating techniques, significant phase correlation was observed between multiple intracavity oscillating wavelengths, with wavelength separations of ?1 nm. The resultant temporal characteristics show a substantial modulation owing to the spectral coupling induced by intracavity-generated four-wave mixing. This result may lead to novel methods for directly generating ultrafast subpicosecond optical pulse sequences with spectrally tailored amplitude and phase characteristics from actively mode-locked semiconductor lasers.

Demonstration of phase correlation in multiwavelength mode-locked semiconductor diode lasers.

This paper presents experimental results of using an inverse bow-tie gain guided semiconductor optical amplifier (SOA) as the optical gain element in a high-power external cavity semiconductor laser. An average output power of 700 mW is demonstrated in continuous-wave (CW) operation while 400 mW of average power is obtained in both passive and hybrid mode-locked operation, with subsequent optical amplification in an identical SOA. The mode-locked laser operates at a repetition rate of 1.062 GHz, owing to the interplay between the gain and saturable absorber dynamics. Optical pulses are generated with a temporal duration of 5 ps, which implies a pulse energy of 376 pJ, and a peak power of 60 W. Further reduction of the optical pulsewidth to 1.3 ps is also achieved by using dispersion compensation techniques. These results show the promise of novel SOA devices for use as gain elements in external cavity semiconductor lasers. The generated output pulse characteristics from mode-locked operation is sufficient for use in novel three-dimensional data storage applications, and in large-scale commercial printing and marking applications.

High-power mode-locked external cavity semiconductor laser using inverse bow-tie semiconductor optical amplifiers

Pulsewidth dependent self‐phase modulation due to ultrafast (∼1 ps) hot‐carrier thermalization is observed for the first time in semiconductor traveling wave amplifiers. The information obtained from this study may play an important role in applications where simultaneous temporal and spectral characteristics of optical pulses is required.

Gerard A. Alphonse

Papers

High-power ultrafast laser diodes

Multiwavelength 10-GHz picosecond pulse generation from a single-stripe semiconductor diode laser

Demonstration of phase correlation in multiwavelength mode-locked semiconductor diode lasers.

High-power mode-locked external cavity semiconductor laser using inverse bow-tie semiconductor optical amplifiers

Hot‐carrier thermalization induced self‐phase modulation in semiconductor traveling wave amplifiers