B. A. Auld

Time-lens producing 1.9 ps optical pulses

A resonant microwave optical phase modulator in LiNbO3 with multiple passes, based on an off‐axis path in a stable optical resonator, is demonstrated as a time‐lens. With 1 W of cw microwave power at 5.2 GHz, 45 ps pulses at 1.06 μm were temporally focused to 6.7 ps (FWHM). Increasing the drive power to 13 W, at 10% duty cycle, produced 1.9 ps pulses. The aperture of the time‐lens is about 31 ps. This is the first demonstration of a useful time‐lens.

Picosecond time-lenses

There is an interesting analogy between the spatial problem of Fresnel diffraction and the temporal problem of first-order dispersion. This space-time analogy was recently extended to propose a time-domain analog to spatial imaging that allows for the distortionless expansion of compression of optical waveforms in time. This process is called temporal imaging. The extension includes the idea of a time-lens as a dual of a spatial lens (regular lens). The time-lens is simply a quadratic optical phase modulator in time, which is approximated by a portion of a sinusoidal phase modulator. Thus, by using phase modulators as lenses and grating pairs as dispersive elements, complete temporal imaging systems can be constructed in exact duality with spatial imaging systems. However, for practically useful time-lenses, considerable modulation is required at fairly high frequencies. The main body of the paper is the detailed design and development of a practical time-lens. This is addressed in Section II, where a resonant microwave modulator is developed based on a LiNbO/sub 3/ loaded waveguide. Multiple passes are obtained through the modulator using an off-axis path in a stable optical resonator. At 5.2-GHz operation, 44 radians of phase modulation is obtained at 1.06-/spl mu/m wavelength for 13 W of microwave power. This corresponds to a time-lens with 31-ps aperture and 1.9-ps resolution. This was confirmed by demonstrating temporal focusing of 45-ps pulses to 1.9 ps. By optimizing the design of the time-lens and better thermal engineering, it may be possible to obtain subpicosecond resolution. >

All‐electronic generation of 880 fs, 3.5 V shockwaves and their application to a 3 THz free‐space signal generation system

We report the first subpicosecond shockwaves ever generated and measured by entirely electronic means. These shockwaves have 880 fs fall times with 3.5 V amplitudes. This was accomplished at T=77 K with a monolithic nonlinear transmission line and diode sampling bridge fabricated on GaAs. We have used these circuits with integrated antennas to generate freely propagating pulses and have detected measurable radiation beyond 3 THz.

2‐picosecond, GaAs photodiode optoelectronic circuit for optical correlation applications

An ultrafast GaAs Schottky photodiode is monolithically integrated with a microwave detector. By using this new optoelectronic circuit in place of a nonlinear crystal in an optical correlation setup, the high‐speed photodiode can measure laser pulse durations without using expensive sampling oscilloscopes. Key advantages are that this circuit works over a broad wavelength range and at low peak optical powers. The correlated temporal response of the circuit is measured to be 1.9 ps full width at half maximum. Due to its wavelength flexibility, cross correlation with different lasers may be performed with this single device.

All-Electronic Subpicosecond Pulses for A 3-Terahertz Free-Space Signal Generation and Detection System

We report the first subpicosecond shock-waves ever generated and measured by electronic circuits. We have used these circuits with integrated antennas to generate and detect freely-propagating THz radiation. The circuits are monolithic nonlinear transmission lines fabricated on GaAs and, for peak efficiency, they operate at liquid nitrogen temperatures. Nonlinear transmission lines (NLTL’s) have been used by several researchers for generating electronic shock-waves with picosecond transition times by compressing the wavefront generated by a ∼0.5 W, ∼5–10 GHz microwave power source.1,2,3 While the literature reflects continual decreases in these transition times, as measured both by diode sampling bridges and by electro-optic sampling, the fastest reported 10%–90% fall time thus far has been 1.4 ps, with a∼5V amplitude.4 However, generating and measuring a sub-picosecond transition with an all-electronic device has been an elusive goal because a fundamental limitation has been the NLTL diode series resistance. By immersing a packaged NLTL into liquid nitrogen, we were able to lower this resistance significantly, thereby producing voltage shock-waves with 880 fs fall times and 3.5 V amplitudes, as measured by an on-chip diode sampling bridge (Figure 1). We have used these circuits with integrated slot antennas to generate freely propagating THz radiation, and we have observed measurable radiation beyond 3 THz.

All-electronic generation and detection of terahertz free-space pulses and their application to a terahertz spectroscopy system

We have developed all-electronic integrated circuits that generate and detect picosecond pulses. We have used these circuits with integrated antennas in a system capable of free- space spectroscopy in the THz regime. With this system, we have measured magnitude and phase transmission characteristics for a variety of samples in the 200 GHz - 1 THz frequency range.