Lute Maleki

Optoelectronic microwave oscillator

We describe a novel oscillator that converts continuous light energy into stable and spectrally pure microwave signals. This optoelectronic microwave oscillator consists of a pump laser and a feedback circuit including an intensity modulator, an optical fiber delay line, a photodetector, an amplifier, and a filter. We develop a quasi-linear theory and obtain expressions for the threshold condition, the amplitude, the frequency, the line width, and the spectral power density of the oscillation. We also present experimental data to compare with the theoretical results. Our findings indicate that the optoelectronic microwave oscillator can generate ultrastable, spectrally pure microwave reference signals up to 75 GHz with a phase noise lower than -140 dBc/Hz at 10 kHz.

Multiloop optoelectronic oscillator

We describe and demonstrate a multiloop technique for single-mode selection in an optoelectronic oscillator (OEO). We present experimental results of a dual loop OEO, free running at 10 GHz, that has the lowest phase noise (-140 dBc/Hz at 10 kHz from carrier) of all free-running room-temperature oscillators to date. Finally, we demonstrate the first fiber-optic implementation of the carrier suppression technique to further reduce the close-to-carrier phase noise of the oscillator by at least 20 dB.

Converting light into spectrally pure microwave oscillation.

We present theoretical and experimental results for a novel oscillator that converts continuous light energy into stable and spectrally pure microwave signals. This optoelectronic oscillator can generate ultrastable spectrally pure microwave reference frequencies as high as 75 GHz with a phase noise lower than 2140 dBcyHz at 10 kHz, independent of oscillation frequency.

DUAL MICROWAVE AND OPTICAL OSCILLATOR

We describe and demonstrate a novel device in which a microwave oscillation and an optical oscillation are generated and directly coupled with each other. With the mutual influence between the microwave and the optical oscillations, we project that this device is capable of simultaneously generating stable optical pulses down to the subpicosecond level and spectrally pure microwave signals at frequencies greater than 70 GHz.

Stabilizing an optoelectronic microwave oscillator with photonic filters

This paper compares methods of active stabilization of an optoelectronic microwave oscillator (OEO) based on insertion of a source of optical group delay into an OEO loop. The performance of an OEO stabilized with either a high-Q optical cavity or an atomic cell is analyzed. We show that the elements play a role of narrow-band microwave filters improving an OEO stability. An atomic cell also allows for locking the oscillation frequency to particular atomic clock transitions. This reports a proof-of-principle experiment on an OEO stabilization using the effect of electromagnetically induced transparency in a hot rubidium atomic vapor cell.

Microsphere integration in active and passive photonics devices

As an important step towards integration of microspheres in compact functional photonics devices, we demonstrate direct efficient coupling of light in and out of high-Q whispering- gallery (WG) modes in silica microspheres using angle- polished single mode fibers. Based on this principle, we present a 1-inch fiber-pigtailed microsphere module that can be used for fiber-optic applications, and a fiber-coupled erbium-doped microsphere laser at 1.55 micrometers . In addition, we report preliminary data on the intensity modulation based on high-Q WG modes in a lithium niobate sphere. We also demonstrate a novel geometry WG-mode optical microcavity that combines Q approximately 107, typical for microspheres, with few-nanometer mode spacing either available in lower quality factor Q approximately 104 microfabricated planar rings.

Tunable, ultra-low phase noise YIG based opto-electronic oscillator

We describe a YIG tuned opto-electronic oscillator with extremely low phase noise. The oscillator can be tuned from 6 to 12 GHz in steps of 3 MHz, and exhibits a phase noise of -128 dBc/Hz at 10 KHz away from the carrier. This is nearly a 30 dB improvement over conventional YIG oscillators, and is derived from the novel approach of the opto-electronic oscillator. To our knowledge, this is the lowest noise performance of any YIG tuned oscillator previously reported.

Photonic-delay technique for phase-noise measurement of microwave oscillators

A photonic-delay line is used as a frequency discriminator for measurement of the phase noise - hence the short-term frequency stability - of microwave oscillators. The scheme is suitable for electronic and photonic oscillators, including the optoelectronic oscillator, mode lock lasers, and other types of rf and microwave pulsed optical sources. The approach is inherently suitable for a wide range of frequency without reconfiguration, which is important for the measurement of tunable oscillators. It is also insensitive to a moderate frequency drift without the need for phase locking.

High-Q microsphere cavity for laser stabilization and optoelectronic microwave oscillator

With submillimeter size and optical Q up to approximately 1010, microspheres with whispering-gallery (WG) modes are attractive new component for fiber-optics/photonics applications and a potential core in ultra-compact high- spectral-purity optical and microwave oscillators. In addition to earlier demonstrated optical locking of diode laser to WG mode in a microsphere, we report on microsphere application in the microwave optoelectronic oscillator, OEO. In OEO, a steady-state microwave modulation of optical carrier is obtained in a closed loop including electro- optical modulator, fiber-optic delay, detector and microwave amplifier. OEO demonstrates exceptionally low phase noise (-140 dBc/Hz at 10 kHz from approximately 10 GHz carrier) with a fiber length approximately 2 km. Current technology allows to put all parts of the OEO, except the fiber, on the same chip. Microspheres, with their demonstrated Q equivalent to a kilometer fiber storage, can replace fiber delays in a truly integrated device. We have obtained microwave oscillation in microsphere-based OEO at 5 to 18 GHz, with 1310 nm and 1550 nm optical carrier, in two configurations: (1) with external DFB pump laser, and (2) with a ring laser including microsphere and a fiber optic amplifier. Also reported is a simple and efficient fiber coupler for microspheres facilitating their integration with existing fiber optics devices.

Low phase noise and spurious level in multi-loop opto-electronic oscillators

We report on substantial improvements of the phase noise, and especially the spurious level of the opto-electronic oscillator (OEO) by using multiple optical loops. We demonstrated a spurious level reduction of more than 30 dB in a dual loop OEO compared with that of a single loop OEO. We found the OEOs closed loop transfer function to describe very well the spurious pattern and to provide an excellent tool for the design of a low spurious multi-loop OEO. The advantages of the multi-loop OEO configuration for a widely tunable OEO will be discussed as well.