Christopher M. DePriest

Toward a photonic arbitrary waveform generator using a modelocked external cavity semiconductor laser

We propose an architecture for photonic arbitrary waveform generation where the phase-locked longitudinal modes of a 12.4-GHz fundamentally modelocked external cavity semiconductor laser are individually modulated. We report photonic synthesis of microwave tones at 37.2 GHz (limited by photodetector bandwidth) with linewidth < 100 Hz and dynamic range 50 dB at 100-Hz resolution bandwidth. We show photonically synthesized 12.4-GHz sine waves with superimposed sinusoidal and pulsed RF modulations, demonstrating the potential for photonic arbitrary waveform generation with the proposed architecture.

Noise in fundamental and harmonic modelocked semiconductor lasers: experiments and simulations

Electric-field correlation measurements of fundamental and harmonic modelocked external cavity semiconductor lasers are presented. Based on these results, an empirical model of a harmonic modelocked pulsetrain is constructed. Using this model, the equivalence between the time-interleaved pulsetrains picture and the supermode picture of a harmonic modelocked pulsetrain is shown. Simulations based on the model are presented showing the key characteristics of modelocked pulsetrains in radio frequency (RF) and optical domains. The fundamental relationship between longitudinal mode linewidth and RF phase-noise corner frequency is delineated. The generated results point to fundamental limitations in timing jitter in modelocked lasers.

Mass-limited, debris-free laser-plasma EUV source

Abstract The development of a laser-plasma EUV line emission source based on frozen water droplet targets which is essentially debris-free and capable of continuous, high-repetition-rate (>1 kHz) operation is described. Created by modest (

High-quality photonic sampling streams from a semiconductor diode ring laser

We report on the development of an ultralow-noise, external-cavity, actively mode-locked semiconductor diode laser for application in next-generation photonic sampling systems. A summary of harmonically mode-locked noise characteristics in a 65-MHz ring cavity is presented through the range of pulse repetition frequencies between 130 MHz and 8.3 GHz (2nd-128th harmonic). Important implications regarding the use of gain-versus-loss modulation as the active modelocking mechanisms are discussed. We also report what are, to our knowledge, the lowest noise characteristics achieved to date for a semiconductor diode laser operating at 10 GHz. Individually optimized results of 0.12% rms amplitude noise (10 Hz-10 MHz), and 43 fs rms residual phase jitter (10 Hz-10 MHz) provide a theoretical resolution of 8.6 bits in a 10-GSPS optical analog-to-digital converter. We have also achieved dispersion-compensated pulsewidths; as short as 1.2 ps, and shown successful operation of a novel phase-locked-loop capable of reducing the rms; residual phase noise by as much as 91% within its response bandwidth. Finally, the first measurements of residual phase noise out to the Nyquist frequency (5 GHz) are presented, providing an upper bound on the rms residual phase jitter of 121 fs (10 Hz-5 GHz).

10-GHz ultralow-noise optical sampling stream from a semiconductor diode ring laser

We report, what is to our knowledge, the lowest-noise pulsetrain produced to date with an actively mode-locked external-cavity semiconductor diode laser. Operating characteristics at 10 GHz include dispersion-compensated pulsewidths as short as 1.2 ps, amplitude noise as low as 0.12% rms, and residual phase noise as low as 43-fs rms. Potential application of such a laser in a next-generation optical analog-to-digital converter would theoretically provide as much as 8.6 bits of resolution, while sampling a 5-GHz waveform at the Nyquist frequency.

Measurement of residual phase noise and longitudinal-mode linewidth in a hybridly mode-locked external linear cavity semiconductor laser

We report measurements of the residual phase-noise knee position and longitudinal-mode linewidth of a hybridly mode-locked external linear cavity semiconductor laser as a function of laser cavity length. Excellent agreement between these measurements suggests a direct relationship between rms pulse-to-pulse timing jitter and average longitudinal-mode linewidth. This relationship leads to a fundamental limit in the timing jitter of mode-locked lasers.

Universality of mode-locked jitter performance

It is shown experimentally that the jitter of actively mode-locked laser pulses is determined by two factors: first, by spontaneous noise associated with cavity loss, and second, by round-trip propagation time. As the round-trip time is increased, a characteristic frequency which defines the high-frequency limit of phase noise decreases. For a comparable round-trip time and cavity loss, the jitter of mode-locked lasers based on diverse gain media, whether semiconductor or erbium ion is universal and independent of the upper-state transition lifetime.

Supermode suppression to below -130 dBc/Hz in a 10 GHz harmonically mode-locked external sigma cavity semiconductor laser

We demonstrate supermode suppression to levels below -125 dBc/Hz and -132 dBc/Hz using Fabry-Perot etalons with finesse values of 180 and 650, respectively, for a 10 GHz harmonically mode-locked external sigma cavity semiconductor laser. The laser was hybridly mode-locked using direct electrical modulation in a compact package without the need for an external modulator.

Ultrahigh-stability photonic sampling streams from an actively-modelocked semiconductor diode ring laser

Summary form only given. Future analog-to-digital conversion needs have inspired recent focus on hybrid optoelectronic systems. The use of short optical pulses for sampling temporal signals promises more accuracy than high-speed electronic comparators. Additional requirements for achieving high precision in high-speed sampling streams are ultralow amplitude and phase noise. Semiconductor optical amplifiers (SOAs) have exhibited proficiency in each of these areas. We report the experimental achievement of optical sampling streams capable of resolving 8.6 bits at a 10 GHz repetition rate. Such accuracy results from ultrashort pulsewidths (1.2 ps), ultralow amplitude noise (0.12% RMS), and ultralow residual jitter (43 fs RMS). A phaselocked-loop (PLL) tested at 2 GHz has further reduced jitter by 91% (from 88 fs to 8 fs).

Modelocked diode lasers for ultra-wideband communications and signal processing

Modelocked semiconductor lasers are used to generate a set of phase locked optical frequencies on a periodic grid. The resulting optical frequency components can be used for communication applications relying on direct detection, dense WDM, coherent detection WDM, OTDM, and OCDMA. In addition, the periodic and phase coherent nature of the optical frequency combs make it possible for the realization of high performance optical and RF arbitrary waveform synthesis. This paper highlights recent results in the use of optical frequency combs for ultrawideband communication and signal processing applications.