Low Noise, High Repetition Rate Semiconductor-based Mode-locked Lasers For Signal Processing And Coherent Communications

This dissertation details work on high repetition rate semiconductor mode-locked lasers. The qualities of stable pulse trains and stable optical frequency content are the focus of the work performed. First, applications of such lasers are reviewed with particular attention to applications only realizable with laser performance such as presented in this dissertation. Sources of timing jitter are also reviewed, as are techniques by which the timing jitter of a 10 GHz optical pulse train may be measured. Experimental results begin with an exploration of the consequences on the timing and amplitude jitter of the phase noise of an RF source used for mode-locking. These results lead to an ultralow timing jitter source, with 30 fs of timing jitter (1 Hz to 5 GHz, extrapolated). The focus of the work then shifts to generating a stabilized optical frequency comb. The first technique to generating the frequency comb is through optical injection. It is shown that not only can injection locking stabilize a mode-locked laser to the injection seed, but linewidth narrowing, timing jitter reduction and suppression of superfluous optical supermodes of a harmonically mode-locked laser also result. A scheme by which optical injection locking can be maintained long term is also proposed. Results on using an intracavity etalon for supermode suppression and optical frequency stabilization then follow. An etalon-based actively mode-locked laser is shown to have a timing jitter of only 20 fs (1Hz-5 GHz, extrapolated), optical linewidths below 10 kHz and optical frequency instabilities less than 400 kHz. By adding dispersion compensating fiber, the optical spectrum was broadened to 2 THz and 800 fs duration pulses were obtained. By using the etalon-based actively mode-locked laser as a basis, a completely self-contained frequency stabilized coupled optoelectronic oscillator was built and characterized. By simultaneously stabilizing the optical frequencies and the pulse repetition rate to the etalon, a 10 GHz comb source centered at 1550 nm was realized. This system maintains the high quality performance of the actively mode-locked laser while significantly reducing the size weight and power consumption of the system. This system also has the potential for outperforming the actively mode-locked laser by increasing the finesse and stability of the intracavity etalon. The final chapter of this dissertation outlines the future work on the etalon-based coupled optoelectronic oscillator, including the incorporation of a higher finesse, more stable etalon and active phase noise suppression of the RF signal. Two appendices give details on phase noise measurements that incorporate carrier suppression and the noise model for the coupled optoelectronic oscillator

Optoelectronic Logic Gate for Real Time Data Mining in a Bit Stream

Invention is an optoelectronic logic gate, which can perform both XNOR and XOR operations at the same time. The main advantage the invention offers is that it can handle multiple input signals simultaneously realizing real parallel processing in multiple channels. The invention has been built and successfully tested. We have demonstrated detecting and locating a 2 bit long target bit sequence inside a streaming input data in real time, without requiring recording of the streaming input data. A prototype is located in CREOL Lab 256. See attached manuscript for details of the invention

High Precision Measurement of the Free Spectral Range of an Etalon

Methods, systems, apparatus and devices for using a modified PDH technique to measure the FSR of an etalon with one part per l0^4 precision. This method is especially useful for etalons with small FSR (less than 10 GHz) because this method does not require a high resolution OSA or tuneable laser. As the ITU grid for DWDM becomes denser, this method will have a larger impact on the FSR measurement of etalons

Optical Frequency Self Sabilization in a Couple of Optoelectronic Oscillator

Methods and devices for a coupled optoelectronic oscillator having optical frequency stabilization. The coupled optoelectronic oscillator includes a harmonically mode-locked laser cavity having a Mach-Zehnder modulator for mode-locking and an intracavity Fabry-Perot etalon to allow only one single supermode to lase, a stabilization loop coupled with the Fabry-Perot etalon to detect changes in the laser cavity optical frequency and generate an error signal to compensate for the frequency change to stabilize the mode-locking of the laser frequency stabilization, and an electrical loop between the laser cavity and the stabilization loop for driving the Mach-Zehnder modulator with the coupled optoelectronic oscillator signal

Two-mode beat phase noise of actively modelocked lasers

An analytic expression for the phase noise spectrum is estimated when two arbitrary longitudinal modes are selected for beating from the output of an actively modelocked laser. A separate experiment confirmed the theory qualitatively. It was found that two- mode beating posseses more phase noise than the beating involving the entire mode spectrum, especially at low offset frequency, even though two mode beating noise is decoupled from the RF oscillator noise to the first order

A near infrared frequency comb for Y+J band astronomical spectroscopy

Radial velocity (RV) surveys supported by high precision wavelength references (notably ThAr lamps and I2 cells) have successfully identified hundreds of exoplanets; however, as the search for exoplanets moves to cooler, lower mass stars, the optimum wave band for observation for these objects moves into the near infrared (NIR) and new wavelength standards are required. To address this need we are following up our successful deployment of an H band(1.45-1.7{\mu}m) laser frequency comb based wavelength reference with a comb working in the Y and J bands (0.98-1.3{\mu}m). This comb will be optimized for use with a 50,000 resolution NIR spectrograph such as the Penn State Habitable Zone Planet Finder. We present design and performance details of the current Y+J band comb.Comment: Submitted to SPIE, conference proceedings 845