Modulation-format agile, reconfigurable Tb/s transmitter based on optical arbitrary waveform generation

Optical arbitrary waveform generation (OAWG) plays a critical role in many applications, such as generating optical ultra-wide band (UWB) signal, optical pulse radar, all-optical temporal differentiator, and test of optical communication system. Although lots of OAWG schemes were reported using mature fiber grating techniques, one of the most promising solutions is prone to be the miniaturization and integration with photonic integrated circuits, such as using indium phosphide (InP) platform, silica on silicon, silicon nitride or silicon platform. In this talk, we review our recent progress on some OAWG schemes using silicon platform and their applications in photonic computing. First, we report an OAWG and high-order photonic differentiator based on a four-tap FIR silicon integrated circuit. By thermally controlling the amplitude and phase of each tap, we obtain several typical waveforms such as triangular waveform, sawtooth waveform, square waveform and Gaussian waveform, etc. Furthermore, we demonstrate first-, second- and third-order differentiation based on the optical pulse shaper, whose spectra were tailored to the transfer functions of temporal differentiators. Especially, our scheme can switch the differentiator patterns from first- to third-order freely on a fixed photonic chip, and this is unable in our previous works such as cascaded microrings or cascaded Mach-Zehnder interferometers (MZIs). Second, we demonstrate radio-frequency arbitrary waveform generation using temporal synthesis. We compare two schemes of cascaded microring resonators and finite impulse response. There functional photnic chip has only millmeter size, low power consumption, and high frequency response. Third, we will demonstrate an OAWG scheme based on superposition of differentiated waveforms. Compared to the first two schemes, this one shows a more compact size and a more flexible operation.

Optical pulse shaping is a widely adopted technique in which intensity and phase manipulation of optical spectral components allow synthesis of user-specified ultrashort pulse fields according to a Fourier transform relationship. Furthermore, mode-locked lasers producing combs of frequency-stabilized spectral lines have resulted in revolutionary advances in frequency metrology. However, until recently pulse shapers addressed spectral lines in groups at low spectral resolution. Line-by-line pulse shaping, in which spectral lines are resolved and manipulated individually, leads to a fundamentally new regime for optical arbitrary waveform generation (O-AWG) in which the advantages of pulse shaping and of frequency combs are exploited simultaneously. Bringing pulse shaping and frequency combs together allows O-AWG with both a controllable ultrafast time structure and long-term coherence. Intuitively, full control of individual frequency comb lines require (1) frequency-stabilized sources to generate stable spectral lines and (2) high-resolution pulse shapers to resolve and control individual spectral lines. O-AWG promises a broad impact both in optical science, allowing for example coherent control generalizations of comb-based time-frequency spectroscopies, and in technology, enabling new truly coherent multiwavelength processing concepts for spread spectrum light wave communications and lidar. This chapter is organized as follows. The significance of spectral line-by-line shaping will be first compared to conventional pulse shaping. Shaper setup will be explained. Line-by-line shaping examples using an actively mode-locked fiber laser will be presented in the second section. Impact of frequency comb frequency instabilities over line-by-line shaped waveforms are explored in the third section. In the fourth section, shaping examples using alternative comb sources are given.

Optical arbitrary waveform generation using the line-by-line pulse shaping technique has been shown to be sensitive to variations in the offset frequency of the input frequency comb due to time-domain waveform interference. Here we present a frequency-domain model that is able to predict waveform changes arising from offset frequency variations. In experiments we controllably shift the frequency of a comb derived from a phase-modulated CW laser, which allows us to quantitatively investigate waveforms generated by pulse shaping as a function of offset frequency. Experimental data are in excellent agreement with the predictions of our frequency-domain model. In addition, we propose and analyze new waveforms designed for monitoring of offset frequency variations by pulse shaping.

We demonstrate optical arbitrary waveform generation and characterization using spectral line-by-line control with high resolution grating based pulse shapers. Such integrated capabilities are the enabling techniques for high-fidelity optical arbitrary waveform generation.

This paper experimentally demonstrates flexible-bandwidth networking by splitting a 500-GHz waveform generated by optical arbitrary waveform generation into its two tributary spectral slices using a liquid-crystal spatial light phase modulator as a wavelength selective switch.

Dynamic optical arbitrary waveform generation and detection in InP photonic integrated circuits for Tb/s optical communications

A phase-modulated CW laser is used to emulate and investigate time-domain waveform noise observed in line-by-line pulse shaping of a mode-locked laser with optical frequency fluctuations.

A monolithically integrated InP chip for optical arbitrary waveform generation (OAWG) and/or pulse-coding/decoding is demonstrated using a 20-GHz AWG pair and 10 high-speed phase modulators. The fabrication and performance of the InP chip will be presented.

We demonstrate optical arbitrary waveform generation using self-injection-locked Kerr micro-combs that are synchronized to an electronic clock via a closed-loop control. We show 200 GBd 32QAM transmission and FMCW LiDAR with an unprecedented resolution of 0.75 mm.

Recently, we proposed the concept of a microring-based optical pulse train generator, which uses a series of microrings coupled to a waveguide and time-interleaves a trigger pulse propagating on this waveguide to generate an optical pulse train. When each ring is electrically modulated, this electronic-photonic integrated circuit (EPIC) can be used for optical arbitrary waveform generation (OAWG) and ultrafast electro-optic (EO) modulation. This paper presents the proof-of-concept experimental demonstration of this technique with two four-stage chip prototypes fabricated on silicon-on-insulator (SOI) substrate. Device fabrication and testing of the chip prototypes are presented. The measurement results show that from a 20-ps-wide input trigger pulse, two circuits generate four sequential pulses at the output with a constant stage delay of 55 ps and 30 ps respectively, which translate into pulse repetition rates of 18 GHz and 33 GHz.

We demonstrate a compact monolithically-integrated InP optical arbitrary waveform generator, consisting of an arrayed waveguide grating pair with 10 GHz channel spacing, 10 high-speed optical amplitude modulators, and 10 high-speed optical phase modulators.

This paper discusses THz bandwidth information and signal processing based on RF-photonic technologies. In particular, we will emphasize integrated circuit approaches to RF-photonics where highly stable THz bandwidth information and signal processing can take place. We will demonstrate THz signal generation by optical arbitrary waveform generation (OAWG), and will describe its inverse process, optical arbitrary waveform measurement (OAWM). Further, we will discuss an RF-photonic lattice filter useful for optical equalization and other THz signal processing replacing traditional electronic digital signal processing which cannot currently scale to THz. The paper will also cover future prospects for the THz information and signal processing by integrated RF-photonic methods.

An integrated multi-wavelength tunable ultra-narrow bandwidth filter on Lithium Niobate substrate is proposed and its performances are analyzed. The filter contains multiple sections of Bragg gratings and waveguides. The waveguides are interleaved between Bragg gratings. A pair of electrodes is fabricated on both sides of each waveguide. Multi-wavelength tunable function can be realized by applying voltages on different electrode pairs. In this paper, tunable filters with three wavelengths and five wavelengths are discussed. The filter with three wavelength contains three pairs of electrodes and the five wavelength filter contains five pairs of electrodes. The number of wavelengths is determined by the number of the electrode pairs. The number of the wavelength can be increased by adding electrode pairs. In the filers a section of waveguide with a pair of electrodes is located in the center of the structure, others are symmetrically distributed on both sides of it. The wavelength difference is influenced by the length of Bragg grating between the electrodes. The longer the Bragg grating, the smaller the wavelength difference. And the bandwidth of each wavelength is around a few pm. The tuning range of the filter is affected by the total length of the Bragg gratings. The longer the total length of the Bragg gratings the wider the tuning range. In addition, the tuning speed of the filter can reach the order of nanosecond due to the simultaneous response of electro-optical effect in Lithium Niobate. It is faster than other filters, based on elastic-optic effect (stress) and thermal effect (the temperature). The integrated multi-wavelength tunable ultra-narrow bandwidth filter based on Lithium Niobate is easy to achieve large-scale integrated. It has great potential application in dense wavelength division multiplexing (DWDM), optical arbitrary waveform generator (OAWG), tunable laser or other fields.

We perform photonic downconversion of microwave signals using an optical frequency comb in a dispersive-delay-line geometry. Programmable analog filtering in the 0-5GHz IF band is achieved through optical arbitrary waveform generation.

Signals in spectrally efficient optical networks can be distorted by the narrowing of the overall bandwidth that occurs when optical add-drop multiplexers are concatenated. In this letter, it is demonstrated that the performance implications of this bandwidth narrowing can be mitigated by precompensation using arbitrary optical waveform generation. The synthesis of the required voltage waveforms for a dual-drive Mach-Zehnder modulator reduces the penalty in receiver sensitivity due to narrow optical filtering from 6.5 to 1.9 dB. Simultaneous precompensation for fiber dispersion is also demonstrated.