Microwave Waveform Generation Research Articles

High Power Photodiodes for Microwave Applications

High Power Photodiodes for Microwave Applications

Photonic Generation of Microwave Waveforms Based on a Polarization Modulator in a Sagnac Loop

An optical microwave waveform generator using a polarization modulator (PolM) in a Sagnac loop is proposed and experimentally demonstrated. Microwave waveforms including a triangular waveform, a sawtooth waveform, and a square waveform, can be generated using a sinusoidal signal to modulate a light wave at a PolM in a Sagnac loop. In the proposed microwave waveform generator, a sinusoidal microwave signal is applied to the PolM in the Sagnac loop. Due to the velocity mismatch, only the clockwise light wave in the Sagnac loop is effectively modulated by the sinusoidal microwave signal at the PolM, and the counter-clockwise light wave is not modulated. Along the clockwise direction, the powers of the odd- and even-order sidebands can be controlled separately by tuning a polarization controller after the PolM. In addition, the output power of the optical carrier can be independently controlled by combining the counter-clockwise and clockwise optical carriers at the output of a polarization beam splitter. As a result, a modulated signal with controllable odd- and even-order sidebands is generated. By applying the modulated signal to a photodetector, a microwave signal with fully controllable odd- and even-order harmonics is generated, which corresponds to a desired microwave waveform. A theoretical analysis is developed, which is validated by an experiment. A triangular, sawtooth, and square waveform with a repetition rate tunable from 2 to 4 GHz is experimentally generated.

Photonic Generation of Frequency Tunable Binary Phase-Coded Microwave Waveforms

A novel photonic approach to generating a precisely π phase-shifted binary phase-coded microwave waveform with ultra-wide frequency tunable range is proposed and experimentally demonstrated. In the proposed system, a polarization modulator (PolM) functions in conjunction with a polarization controller (PC) and an optical polarizer (Pol) as an equivalent Mach-Zehnder modulator (MZM) with the bias point switchable by applying a binary-coding signal to the PolM. To generate a phase-coded microwave signal at a specific microwave frequency, the binary-coding signal is combined with a microwave signal at that frequency and applied to the PolM. By switching between the two quadrature transmission points or the maximum and the minimum transmission points, a phase-coded microwave waveform at the fundamental or doubled frequency is generated. The proposed technique is experimentally evaluated. A phase-coded microwave waveform at the fundamental and doubled frequency is generated. The tunability of the approach is also experimentally demonstrated.

Arbitrary Microwave Waveform Generation Based on a Tunable Optoelectronic Oscillator

Photonic generation of a phase-coded or frequency-chirped microwave waveform with a tunable microwave carrier frequency using a frequency-tunable optoelectronic oscillator (OEO) is proposed and experimentally demonstrated, for the first time to the best of our knowledge. In the proposed system, the tunable OEO has functions to generate a frequency-tunable microwave signal and to output an optical sideband. The optical sideband and a portion of the light wave from the OEO laser source are sent to a polarization modulator (PolM), with their polarization directions aligned with the two principal axes of the PolM. An electrical signal is applied to the PolM, and two complementary phase-coded or frequency-chirped light waves are generated which are converted to an electrical signal by beating the light waves at a high-speed photodetector. The key significance of the technique is that a phase-coded or frequency-chirped microwave waveform with a tunable microwave carrier frequency and a reconfigurable phase-coding or frequency-chirping pattern can be generated without using a separate microwave source. The technique is experimentally verified. The generation of a binary- and a polyphase-coded microwave waveform with a microwave carrier frequency at 10 and 15 GHz is demonstrated. The generation of a linearly frequency-chirped microwave waveform with a chip rate of 20.98 GHz/ns at a 10-GHz carrier frequency and 22.5 GHz/ns at a 15-GHz carrier frequency is also achieved.

Photonic generation of microwave waveforms with wide chirp tuning range

We show analytically as well as demonstrate experimentally an approach to generate microwave waveforms with wide chirp tuning range. The approach is based on the interference of two temporally-stretched pulses which are time-delayed with respect to each other and having different frequency chirp. This approach is realized by an unbalanced Mach Zehnder Interferometer (MZI) incorporating a linearly-chirped fiber-Bragg-grating (LCFBG) whose group-delay-dispersion (GDD) can be tuned across a wide range. In general, tuning the GDD of the LCFBG changes the chirp rate of the generated microwave waveform and tuning the relative time-delay between the interferometer arms changes the center frequency of the generated microwave waveform. Balanced photodetection is also implemented to obtain DC-free microwave waveforms. Based on this approach, we demonstrate the generation of microwave waveforms with different center frequencies and with the chirp rates ranging from∼−126.7GHz/ns to ∼+120.8GHz/ns, including the zero-chirp case.

Continuously Tunable Chirped Microwave Waveform Generation Using a Tilted Fiber Bragg Grating Written in an Erbium/Ytterbium Codoped Fiber

An optical approach to generating continuously tunable chirped microwave waveforms using a tilted fiber Bragg grating (TFBG) written in an erbium/ytterbium (Er/Yb) codoped fiber is proposed. By pumping the TFBG, the magnitude and group delay responses of the cladding mode resonances are changed, which can be used to implement a photonic microwave delay-line filter with increasing or decreasing tap spacing. If an ultranarrow pulse is sent to the photonic microwave delay-line filter, a pulse burst with increasing or decreasing pulse spacing is generated. The photodetection of the pulse burst would lead to the generation of a chirped microwave waveform. The proposed technique is demonstrated by an experiment in which a chirped microwave waveform with a tunable chirp rate from 1.8 to 7 GHz/ns is generated.

Photonic generation of microwave arbitrary waveforms

In this paper, techniques to generate microwave arbitrary waveforms based on all-fiber solutions are reviewed, with an emphasis on the system architectures based on direct space-to-time pulse shaping, spectral-shaping and wavelength-to-time mapping, temporal pulse shaping, and photonic microwave delay-line filtering. The generation of phase-coded and frequency-chirped microwave waveforms is discussed. The challenges in the implementation of the systems for practical applications are also discussed.

Tilted Fiber Bragg Grating for Chirped Microwave Waveform Generation

A tilted fiber Bragg grating (TFBG) as an optical spectral shaper to generate a chirped microwave waveform in a spectral-shaping and wavelength-to-time (SS-WTT) mapping system is proposed and demonstrated. The key component in the system is the TFBG, which has multiple resonant peaks with linearly increasing spacing in its transmission spectrum. By incorporating a TFBG into an SS-WTT system, a chirped microwave waveform is generated with the chirp rate determined by the tilt angle of the TFBG. A proof-of-concept experiment is carried out. Two TFBGs with tilt angles of 10 and 4 are fabricated and employed to generate two chirped microwave waveforms with chirp rates of 0.00700 and 0.05956 GHz/ps, respectively.

An Unbalanced Temporal Pulse-Shaping System for Chirped Microwave Waveform Generation

An unbalanced temporal pulse-shaping (TPS) system for chirped microwave waveform generation is proposed and demonstrated. The proposed system consists of an ultrashort pulsed source, a Mach-Zehnder modulator and two dispersive elements. The dispersions of the two dispersive elements are opposite in sign, but not identical in magnitude. The entire system is equivalent to a conventional balanced TPS system with two complementary dispersive elements for real-time Fourier transformation and a third dispersive element to achieve a second real-time Fourier transformation. The key contribution of this work is that the third-order dispersion of the dispersive elements is considered, which leads to the generation of a frequency-chirped microwave waveform. A theoretical analysis is performed in which a mathematical model that relates the second- and third-order dispersion of the dispersive elements and the chirp rate of the generated microwave waveform is developed. The theoretical model is then verified by numerical simulations and an experiment. A chirped microwave waveform with different chirp rates of -0.0535 and 0.715 GHz/ns by tuning the third-order dispersion using a tunable chirped fiber Bragg grating is experimentally demonstrated.

The evolving optical frequency comb [Invited

In the past decade we have witnessed remarkable advances associated with the frequency stabilization of the comb present in the output of a mode-locked femtosecond laser. While proving itself to be fantastically successful in its role as the “gears” of optical atomic clocks, the optical frequency comb has further evolved into a valuable tool for a wide range of applications, including ultraviolet and infrared spectroscopy, frequency synthesis, optical and microwave waveform generation, astronomical spectrograph calibration, and attosecond pulse generation, to name a few. In this review, I will trace several of these developments while attempting to offer perspective on the challenges and opportunities for frequency combs that might lie ahead in the next decade.

Large Time-Bandwidth Product Microwave Arbitrary Waveform Generation Using a Spatially Discrete Chirped Fiber Bragg Grating

We propose and experimentally demonstrate an approach to generating large time-bandwidth product (TBWP) microwave arbitrary waveforms based on optical pulse shaping using a single spatially discrete chirped fiber Bragg grating (SD-CFBG). The SD-CFBG functions to perform simultaneously spectral slicing, frequency-to-time mapping, and temporal shifting of the input optical pulse, which leads to the generation of an optical pulse burst with the individual pulses in the burst temporally spaced by the time delays determined by the SD-CFBG. With the help of a bandwidth-limited photodetector (PD), a smooth microwave waveform is obtained. The SD-CFBG is fabricated using a linearly chirped phase mask by axially shifting the photosensitive fiber to introduce a spatial spacing between two adjacent sub-gratings during the fabrication process. By properly designing the fiber shifting function, a large TBWP microwave arbitrary waveform with the desired frequency chirping or phase coding can be generated. An equation that relates the fiber shifting function and the microwave waveform frequency chirping is derived. The photonic generation of large TBWP microwave waveforms with a linear, nonlinear and stepped frequency chirping is experimentally demonstrated.