UCF’s Delfyett Inducted into National Academy of Engineering
#RealWorldHonor
UCF’s Delfyett Inducted into National Academy of Engineering
#RealWorldHonor
Research Terms
| Director |
Peter Delfyett |
| Phone | 407-823-6812 |
| Website | https://www.creol.ucf.edu/townes-laser-institute/ |
| Mission | To develop the next generation of laser light engines for applications in medicine, advanced manufacturing and defense applications. These include: in laser development and laser-based technologies at UCF, in ultra-fast laser technologies, laser materials processing, novel optics for high power lasers, fiber laser development, laser-based sensing, laser-plasma EUV sources, and other related topics.To develop the next generation of laser light engines for applications in medicine, advanced manufacturing and defense applications. These include: in laser development and laser-based technologies at UCF, in ultra-fast laser technologies, laser materials processing, novel optics for high power lasers, fiber laser development, laser-based sensing, laser-plasma EUV sources, and other related topics.
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The University of Central Florida invention is a system that produces a spectrally pure electrical oscillation using an optoelectronic oscillator (OEO) loop. With the loop, the system modulates a continuous-wave (CW) laser to form an electro-optic modulated comb that is then conditioned by a saturable absorber, amplified and filtered. It is used as a seed for generating white light and then interfered with itself for self-referencing. The system is self-starting, self-oscillating, and self-referencing, allowing for size, weight, power, and cost improvements.
Partnering Opportunity: The research team is seeking partners for licensing, research collaboration, or both.
Stage of Development: Prototype available.
Researchers at the University of Central Florida have invented an optoelectronic oscillator (OEO) that replaces an RF filter with an interferometer, specifically a high finesse Fabry-Perot etalon, as the mode selector. The substitution provides lower phase noise and higher RF frequency stability due to the higher Q and ultralow temperature dependency of the Fabry-Perot etalon. This invention can enhance radar and signal intelligence, clock recovery, and communication broadcasting and receiving.
OEOs provide a continuous, high-quality factor (Q) modulated signal in order to obtain high spectral purity. They are used for a variety of purposes, including a carrier wave for communications, and radar emissions. Most OEOs use an RF filter as the mode selector for signal generation.
However, there are some drawbacks with using the standard OEO. To compensate for the losses in the RF loop, a high gain RF amplifier is needed. It is expensive to make an ultra-narrow bandwidth RF filter required for a long optical delays, and in addition, the loss from the RF filter decreases the cavity Q of the OEO, which increases phase noise. RF amplifiers also suffer from small temperature fluctuations resulting in a domino effect of adverse effects: fluctuations in peak position resonance change the RF filter phase, which then affects the microwave signal's total round-trip time, and ultimately changes the oscillation frequency.
Technical Details
In this design, a 10.287 GHz OEO is coupled with a 1000 finesse Fabry-Perot etalon as the resonant mode selector. This sealed, ultralow expansion quartz etalon is protected from temperature, air pressure, and other environmental changes. This design also includes the standard OEO components: an electro-optic modulator (EOM), an optical delay line, a photodiode, and an RF amplifier. The periodic transmission function of the etalon only allows the oscillation of optical frequencies, which are separated by the etalon's free spectral range (FSR). This function also eliminates the frequencies outside the resonance width. Additionally, the microwave oscillation frequency is determined by the etalon's FSR.
Photonic frequency comb technology can improve applications in the field of multi-heterodyne spectroscopy, including data harvesting and pattern recognition. Previous methods of stabilizing frequency combs are highly complex and inherently generate noise, but by applying the H?nsch-Couillaud (HC) method, formerly only applicable to single-mode systems, UCF researchers significantly reduced the complexity and thus eliminated the noise. The inventors' effective use of the HC method on an injection-locked, harmonically mode-locked system to generate and stabilize a high-finesse optical frequency comb eliminates the unwanted phase modulation sidebands of the conventionally used Pound-Drever-Hall (PDH) method.
Existing phase modulation techniques for generating 10 GHz frequency combs have been limited to less than 1nm. This technology extends the bandwidth range to more than 9 nm, while providing tunable comb spacing, a benefit not offered by intracavity etalon-based alternatives. Additionally, the combs' narrow linewidth means low noise regardless of cavity resonance width.
Technical Details
This invention consists of a commercially available semiconductor optical amplifier in an external fiber ring cavity and a Mach-Zehnder intensity modulator driven at the desired pulse repetition rate and frequency comb spacing for the intended application, both acting as polarization discriminating devices. Further, the method involves the use of two couplers for laser output and injection input, with multiple polarization controllers and an optical isolator to ensure unidirectional operation. The inventors' prototype, for example, incorporates a continuous wave (CW) narrow linewidth (~1 kHz) laser at 1550 nm as the injection seed source, and a variable optical attenuator for injected power control. The injected tone experiences a phase shift while interacting with the cavity. Signals are then rotated via polarization controller(s) to interfere with both outputs of a fiberized polarization beam splitter. A balanced photodetector takes the difference between the two signals to produce an error signal.
Researchers at the University of Central Florida have developed an ultralow noise portable frequency comb that improves on a prior invention (US 7,697,579). The new invention uses a high finesse etalon as an integral part of the mode-locked laser that simultaneously stabilizes the carrier offset, produces sub-Hertz level axial mode components, and provides important error signals that enable octave spanning optical frequency division?all within a single laser. This streamlined system fits in a standard rack-mountable chassis with a demonstrated lowest phase noise at 10 GHz, and 1550 nm from this type of source. Within this system, there is no need for an f-2f interferometer, no second harmonic generation stages for stabilization, or a separate CW laser locked to an etalon. Because of the higher efficiency of this invention, it is more easily deployable in the field and with a less strenuous system calibration.
Currently available technologies that generate a low noise 10 GHz pulse train with RF phase noise use optical frequency division, but as a result, suffer from stabilization and calibration difficulties. The conventional optical frequency divider is comprised of four main components: a mode-locked laser, a separate continuous wave (CW) laser, a nonlinear f-2f interferometer, and an optical pulse train interleaver.
Technical Details
The UCF invention includes an ultralow noise, portable frequency comb device based on a fiber cavity mode-locked laser using semiconductor optical amplifiers as the gain elements, combined with an environmentally stable macroscopic Fabry-P?rot etalon as a secondary optical reference. This device uses regenerative mode-locking, thus the laser is not slaved to an electronic reference. The ultrahigh finesse etalon, located inside the laser, serves as the stable optical reference to which all error signals and stabilization are referenced. In comparison to current technologies that create optical linewidths at the sub Hz level, this device creates ultra-narrow, optical comb lines with Hz level linewidths. This design decouples and independently stabilizes the carrier envelope offset frequency and repetition rate fluctuations by using a linear optical frequency division that reduces RF noise by a factor of 10log(N2), where N is the optical bandwidth of the mode-locked laser divided by the pulse repetition rate.
Researchers at the University of Central Florida have developed a unique architecture for an electro-optic modulation (EOM) tunable comb generator that combines a photonically filtered optoelectronic oscillator (OEO) with a series of external phase modulators. Using the ultra-narrow resonances of a 100,000-finesse Fabry-Perot etalon (FPE), the new design enables oscillation frequency and comb tooth spacing for spectrally flat, broadband, widely spaced frequency combs. For example, the new architecture has produced spectra as broad as approximately 5 nanometers (nm), while other OEO-driven comb generators have only produced optical combs spanning less than 2 nm.
Most optical frequency comb sources require an external radio frequency (RF) reference such as a high-frequency RF synthesizer, which can be costly. However, with the new architecture, the comb generator creates its own RF source to drive the modulators, eliminating the need for an external reference signal. Also, the FPE enables extremely selective filtering, enhanced OEO frequency stability, and narrower optical linewidths. Incorporating the phase modulators outside the OEO cavity allows for independent tuning and optimization of the comb spectral phase for ultrashort pulse generation without affecting oscillation.
Technical Details
The UCF invention consists of an OEO-EOM comb architecture that generates tunable electro-optic combs using an optoelectronic oscillator. In an example configuration, the architecture comprises three subsystems:
Experimental results demonstrate regeneratively-created electro-optic combs whose comb teeth spacing is tunable to 7.5 GHz, 9 GHz, 10.5 GHz and 12 GHz?with the center comb tooth linewidths running hundreds of hertz. When using linear pulse compression, the system demonstrates ultrashort pulses with picosecond-level autocorrelation pulse widths at a repetition rate of 10.5 GHz.
Partnering Opportunity
The research team is looking for partners to develop the technology further for commercialization.
Stage of Development
Prototype available.
Researchers at the University of Central Florida have invented a chip-scale optical-to-RF link technology that clears a path for integrated photonics. Using a novel harmonic multitone injection locking technique, the invention down-converts frequency combs from the optical domain (>120GHz to THz) into the microwave domain (10s of GHz), where it can be easily photo-detected and controlled. Thus, as a timing signal generator or optical clock, the new technology provides enhanced timing precision for Position, Navigation and Timing (PNT) applications, such as secure communications in military GPS-denied environments. It may also provide a precise timing reference for high-bandwidth coherent telecommunications or a wavelength reference for metrology. Compared to existing technologies, the invention is simpler, since it relies on the natural phase-lock effect from the optical injection locking process instead of electronic phase-locked loops. It is also more robust, since it inherits from the stability of the injection locking process. Finally, the system is more efficient, since it requires little optical power for the harmonic injection locking process.
Technical Details
With its unique harmonic multi-tone injection locking technique, the invention expands the concept of optical injection locking, in which a slave laser is synchronized to a master laser. The figure illustrates the new technique involving a widely-spaced optical frequency comb (OFC) at nf_rep and a slave mode-locked laser (MLL) at f_rep. The master OFC injects multiple tones into the slave MLL at a harmonic of the fundamental repetition rate (f_rep), thereby down-converting a set of millimeter-wave or THz range separated optical tones into the GHz/microwave domain. When the multiple tones of the master laser coincide with adjacent comb lines of the MLL, the repetition rate stability from the master is transferred to the slave, as well. The technique effectively reduces the linewidth of the individual axial modes, stabilizes the repetition rate, and reduces the RF spectrum phase noise. The architecture is compatible with current fabrication processes and offers a SWaP (size, weight and power) system with a dramatic increase in accuracy and robust, long-term stability.
Harmonic Injection Locking for a Direct Optical to RF Link
Researchers at the University of Central Florida have developed a method for producing a stable optical clock signal of more than 12.4GHz using the classical wave phenomenon of frequency beating.
Technical Details
Commonly, where an optical clock is needed, an electronic one is as well, and the invention proposed herein offers both simultaneously. The design presented here produces a beat note created through the paring of two mode-locked pulses.
Fabry-Perot interferometers, or simply etalons, have been used for many years to select and stabilize the wavelength of tunable diode lasers for Dense Wavelength Division Multiplexed (DWDM) systems. The etalon consists of two parallel flat semi-transparent mirrors separated by a fixed distance. Light that enters the etalon undergoes multiple reflections and the interference of the light emerging from the etalon during each bounce causes a modulation in the transmitted and reflected beams. The transmission spectrum of an etalon will have a series of peaks spaced by the free spectral range (FSR), which is the spacing in optical frequency or wavelength between two successive reflected or transmitted optical intensity maxima or minima. To match the transmission channels of an etalon with the International Telecommunication Union (ITU) grid, precise measurement of the free spectral range (FSR) of the etalon is highly critical. Most reported works are based on the mapping out of the transmission spectrum as the injected laser wavelength is tuned. These techniques are quite simple and fairly precise, allowing up to 4 parts per million of error for a 100 GHz free spectral range etalon. However, the precision is fundamentally limited by the resolution of the optical spectrum analyzer or the tunable laser used, making it very difficult to apply to etalons with an FSR smaller than 10 GHz.
Technical Details
The Pound-Drever-Hall (PDH) technique gives an electronic readout signal of the resonance condition of an optical cavity relative to an incident laser frequency. In recent years, this technique has been well known to stabilize the laser wavelength using an etalon as a frequency reference. The UCF invention uses a simple modification of the PDH technique to measure the FSR of etalons with precision easily exceeding one part of 104, regardless of the size of the FSR. As the ITU grid for DWDM becomes denser, this method will have a significant impact on the FSR measurement of etalons. Moreover, this innovative technology allows for high resolution measurement of the FSR of an etalon without the use of a high-resolution optical spectrum analyzer (OSA) or tunable laser, which would limit the precision measurement.
Researchers at the University of Central Florida have invented a system that introduces coherent optical signal processing via spectrally phase-encoded optical frequency combs for real-time optical filters and pattern recognition. As the amount of digital information and communication increases, timely and accurate data collection for software-based evaluation and correlation becomes increasingly more difficult. The increase in difficulty arises from three main issues: the sheer volume of the data being generated; the nature of the desired information relative to the comparison set; and the desired information that lies in the noise of the overall data set being evaluated. Thus, an integration of fundamental advancements in the generation and recognition of optical patterns to improve the speed of high-performance computing and data mining is needed. Existing high performance computer designs face the historical challenges of generating enormous amounts of heat, processing latencies measured in tens of nanoseconds and poor general processing flexibility. One lossless approach to overcoming these limitations is to perform the computing function with light. However, for the last three decades optical computing has been the perennial technology of tomorrow because of the persistent limitations imposed by the lack of programmability and the slow translation of electric data into optical regime.
Technical Details
The UCF invention is a robust, compact, scalable optical signal processing system for enhancing the speed of high-performance computing by more than two orders of magnitude. This is based upon the integration of fundamental advancements in the generation and relational recognition of optical patterns. The invention demonstrates a clear and achievable path towards making programmable optical computing a reality by overcoming historical barriers.
Researchers at the University of Central Florida have developed an innovation that implements multiple, simultaneous input signals while searching and detecting a target code in multiple channels at the same time. This way, input data can be processed in real-time, and allows for true parallel processing in multiple channels. This parallel processing provides an advantage over other approaches, both all-optical and electrical, and enables n-bit pattern extraction in real-time streaming data. Currently available all-optical logic gates cannot process multiple signals at different wavelengths simultaneously as conventional logic gates are wavelength-dependent.
Boolean exclusive OR (XOR) and exclusive NOR (XNOR) logic gates are used for data mining, pattern extraction, data traffic control, and data routing in telecommunication applications due to their usefulness in label switching, parity checking, and pattern recognition.
Alternatives founded on nonlinear loop mirrors do not match the innovation?s higher power efficiency. Those based on semiconductor nonlinearities cannot match its ability to maintain signal quality in the case of on-off keying (OOK) formatted input signals.
Technical Details
The new optoelectronic logic gate is wavelength-independent due in part to interferometric switches as comparators of optical bits and electrical bits. In the processing imprint stage, the logic gate is separated into two parts consisting of a single interferometric switch for single bit operation to imprint electrical input data on an optical signal, and the comparator stage, consisting of two parallel interferometric switches wherein input data is superimposed on the optical signals compared with target data in the electrical realm. The comparator stage is the key to simultaneous processing, as all relative timing signals can be sent to it at the same time. With the optoelectronic logic gate, a user can locate and detect real-time streaming input data without needing prior knowledge of the data other than its rate. The setup can be scaled with the inclusion of multiple interferometric switches and multiple mode-locked optical frequencies thus detecting much longer target patterns, faster, in streaming data.
Researchers at the University of Central Florida have developed a new linear modulator with potentially infinite SFDR and multi-gigahertz bandwidth that offers possible negative insertion loss and very low Vpi, in the range of few milivolts, compared to existing technologies. Current linear modulators offer limited bandwidth and spurious-free dynamic range (SFDR) as electro-optic modulators and power handling as directly modulated lasers--also incurring high insertion loss and high Vpi. While a conventional method for linearizing modulators uses a complicated feedforward electrical circuit to correct for nonlinearities, with still-limited SFDR, the new technology offers pure linear response without the need for a correcting circuit. This linear optical modulator is useful in signal processing, fiber optic communication, frequency comb sources, computer interconnect, radio frequency communication, and radio frequency synthesis.
Technical Details
The UCF linear optical modulator achieves a linear response by phase modulating the output of an injection locked slave laser, or modulating the resonance of an injection locked slave laser, and combining the modulated output with the injection source signal from the master laser. The modulator uses a resonant cavity in one arm of a Mach Zehnder interferometer. The output frequency of the resonant cavity device, the same as the injected signal, collects a phase related to the frequency difference--the resonant cavity frequency and the detuning of the injected cavity frequency--leading to the arcsine of the detuning. Combining the arcsine phase modulated signal with a coherent signal creates a detected signal following the standard interferometer expression.
