Brian H. Kolner

Electrooptic sampling in GaAs integrated circuits

Electrooptic sampling has been shown to be a very powerful technique for making time-domain measurements of fast electronic devices and circuits. Previous embodiments relied on a hybrid connection between the device under test and a transmission line deposited on an electrooptic substrate such as LiTaO 3 . The hybrid nature of this approach leads to device packaging difficulties and can result in measurement inaccuracies and performance degradation at very high frequencies. Since GaAs is electrooptic and an attractive material for high speed devices, we have devised an approach of direct electrooptic sampling of voltage waveforms in the host semiconductor. In this paper, we review the principles and limitations of electrooptic sampling and discuss this new noninvasive technique for electronic probing with applications to characterizing high speed GaAs circuits and devices.

Temporal imaging with a time lens

We extend the well-known analogy between the problems of paraxial diffraction in space and dispersion in time to optical pulse compression and propose a time-domain analog to spatial imaging that allows for the distortionless expansion or compression of optical power waveforms. We call this new concept temporal imaging and derive equivalent expressions for the focal length and the f-number of a time lens and the magnification of an imaging system. It should now become possible, with a temporal microscope, to expand ultrafast optical phenomena to a time scale that is accessible to conventional high-speed photodiodes.

Intermodulation distortion and compression in an integrated electrooptic modulator.

We have characterized the intermodulation distortion and compression properties of an integrated optical modulator at microwave frequencies by measuring the third-order intercept and 1-dB compression points. Values of +30.0 and +21.4 dBm, respectively, were measured and agree well with theory. When operated in the shot-noise-limited regime, these devices can have spurious free dynamic ranges in excess of 100 dB, making them attractive as potential alternatives to conventional diode mixers in special applications.

UPCONVERSION TIME MICROSCOPE DEMONSTRATING 103 MAGNIFICATION OF FEMTOSECOND WAVEFORMS

We present the operational principles and results of a temporal imaging system, configured as a time microscope, that achieves 103 x magnification of waveforms with 300-fs resolution and a 5.7-ps field of view. The quadratic-phase time-lens element is realized by upconversion of the dispersed input waveform with a linearly chirped 5-THz bandwidth pump. The system allows expansion of ultrafast optical waveforms to a time scale that is directly accessible with slower conventional technology, in real time, on a single-shot basis.

High-dynamic-range laser amplitude and phase noise measurement techniques

We describe techniques for making sensitive and high-dynamic-range measurements of laser amplitude and envelope phase noise (timing jitter) in the frequency domain at the shot-noise limit. Examples of amplitude noise measurements on continuous-wave argon-ion and diode-pumped solid-state lasers used for pumping a femtosecond Ti:sapphire laser are presented. Amplitude and phase noise measurements for the Ti:sapphire laser are also presented, showing correlation between pump laser amplitude modulation (AM) spectra and the resulting AM and phase noise. Characteristics of the measurement system components are discussed, along with examples of the impact these have on achieving reliable high-dynamic-range measurement capability.

TEMPORAL MAGNIFICATION AND REVERSAL OF 100 GB/S OPTICAL DATA WITH AN UP-CONVERSION TIME MICROSCOPE

We have developed an up‐conversion time microscope capable of expanding ultrafast optical wave forms to a time scale accessible to ordinary sampling oscilloscopes. In this system, a 100 Gb/s optical word is magnified (slowed down) to a rate of 8.55 Gb/s with a time lens placed between two dispersive delay lines. The time lens is a nonlinear crystal which mixes the dispersed data with a linearly chirped pump pulse thus imparting a linear frequency sweep to the unconverted wave form. A second dispersive delay line completes the arrangement and forms the temporal analog of a single lens spatial imaging system resulting in a time reversed wave form with a magnification M=−11.7.

Spectral phase-encoded time-spreading (SPECTS) optical code-division multiple access for terabit optical access networks

This paper discusses design, simulation, and experimental investigations of optical-code-division multiple-access (O-CDMA) networking using a spectral phase-encoded time spreading (SPECTS) method. O-CDMA technologies can potentially provide flexible access of optical bandwidths in excess of 1Tb/s without relying on wavelength- or time-division-multiplexing modules, provided that they overcome the interference caused by other users broadcasting over the same channel, called multiuser interference (MUI). This paper pursues theoretical and experimental methods to mitigate the MUI. Analysis shows that nonuniform phase coding can increase the orthogonality of the code set, thereby reducing the impact of the MUI. The experiment conducted in a SPECTS O-CDMA testbed incorporating a highly nonlinear thresholder demonstrated error-free operation for four users at 1.25-Gb/s/user and for two users at 10-Gb/s/user.

Active pulse compression using an integrated electro‐optic phase modulator

We describe a pulse compression technique that uses integrated electro‐optic phase modulators to linearly chirp optical pulses for compression by a dispersive delay line. In contrast to passive chirp techniques such as self‐phase modulation, this approach of active pulse compression does not depend on the optical power and thus shows promise for application to low‐power solid‐state lasers as an alternative to mode locking for realizing compact picosecond sources. We have demonstrated this technique by compressing the pulses from a mode‐locked neodymium:yttrium aluminum garnet laser from 100 to 45 ps.

An eight-user time-slotted SPECTS O-CDMA testbed: demonstration and simulations

This paper demonstrates an eight-user 9 Gb/s/user time-slotted spectral phase-encoded time-spreading (SPECTS) optical code division multiple access (O-CDMA) testbed. Experimentally measured performance is compared to numerical simulations. The testbed employs a novel compact fiber-pigtailed bulk-optics setup that utilizes a single two-dimensional (2-D) phase modulator for encoding multiple channels, each with a unique 64-chip Walsh code. The time-gated receiver is composed of a nonlinear optical loop mirror (NOLM) and a nonlinear thresholder each utilizing a highly nonlinear fiber (HNLF) as the nonlinear element. The testbed operates error free with up to six users and at a bit error rate BER<10/sup -9/ for eight simultaneous users. Careful modeling of each component in the testbed allows a close match between simulated and experimentally measured testbed performance.

High-fidelity line-by-line optical waveform generation and complete characterization using FROG

A stable optical frequency comb with 20-GHz spacing is shaped by a compact integrated silica arrayed waveguide grating (AWG) pair to produce optical waveforms with unprecedented fidelity. Complete characterization of both the intensity and phase of the crafted optical fields is accomplished with cross-correlation frequency resolved optical gating (XFROG) which has been optimized for periodic waveforms with resolvable modes. A new method is proposed to quantify, in a single number, the quality of the match in both the amplitude and phase between the measured optical waveform and the target waveform.