Optical format conversion technologies have attracted a lot of attention to bridge the different optical networks employing different formats. In this paper, the advances of optical format conversion technologies are introduced and reviewed. Through analyzing the optical network architecture and modulation technology development, we focus on the format conversions between the signals with one dimensional and two dimensional constellations. The important enabling technologies for flexible constellation manipulation are introduced in detail, including the linear and nonlinear optical effects-based functions. Then the key format conversion researches are reviewed in four categories: one-to-one conversions, optical aggregations, optical de-aggregations, and optical interconversions. Finally, the current issue and future trend of this research field is analyzed and discussed.

Whispering-gallery-mode (WGM) resonator with high-quality factor ( Q ) is a key platform for a wide range of fields including nonlinear optics, biosensing and quantum photonics. In this work, a packaged silica microrod resonator (PSMR) with ultrahigh- Q of $\bf 9.0\times 10^{8}$ is experimentally demonstrated. Ultrahigh four-wave mixing conversion efficiency of -8.6 dB at a pump power of 27 mW is achieved within this ultrahigh- Q PSMR. Furthermore, this PSMR shows high stability of resonant wavelength shift within 0.032 pm. This work suggests that the PSMR may be a promising platform for optical signal processing and quantum photonics.

In this paper, we report a novel optical data fragmentation multipath (ODFM) scheme for coherent optical communication based on electrical signal processing in simulation. Under the control of a pseudo-random sequence (PRBS), we randomly disperse the user data and assign them to paths corresponding to different wavelengths for transmission. To reduce the hardware complexity of the system and the requirements for receiver sensitivity, we adopt binary phase shift keying (BPSK) modulation and homodyne coherent detection in the scheme. To verify the feasibility of the proposed ODFM scheme, we demonstrated an error-free transmission through 40 km fiber with 10 Gbps hopping rate and 10 Gbps data rate by the simulation tools. The proposed scheme can be widely used in the physical layer secure communication of backbone network, large-scale data transmission and physical layer encryption of free space optical (FSO) communication.

A photonic multi-format background-free binarily modulated microwave signal generator using a single dual-polarization dual-parallel Mach–Zehnder modulator is proposed and demonstrated. The proposed generator features good reconfiguration and switchability. By simply adjusting the direct current biases of the modulator, amplitude shift keying (ASK), phase shift keying (PSK) and frequency-shift keying (FSK) microwave signals can be generated. Benefiting from the complementary intensity modulation, there is no residual baseband modulated signal in the generated binarily modulated signals. The system does not involve any optical or electrical filters, which ensures good tunability of the generator. By changing the frequency of the driven microwave carrier and bit rate of the electrical coded signal, the frequency and rate of the generated multi-format signals can be adjusted accordingly. The multi-format switchable signal generator has great potential in multi-functional communication and radar systems.

We propose and demonstrate a highly efficient photonic-assisted microwave signal harmonic frequency down-conversion using four-wave mixing (FWM) in a silicon waveguide with a reverse-biased P-i-N junction. In the proposed method, two Mach-Zehnder modulators (MZMs) are driven by a radio frequency (RF) signal and a low-frequency local oscillation (LO) signal, separately. Then, the modulated LO signal is injected into the silicon waveguide. Besides, the FWM phenomenon occurred in the integrated waveguide due to the doped regions of the junction can increase the efficiency of free carrier removal from the waveguide region. As the applied bias voltage on the silicon waveguide is increased, the generated harmonic sidebands are further enlarged. Correspondingly, the conversion efficiency is up to 12.8 dB with the bias voltage of 30 V. The silicon waveguide is fully packaged with a grating coupling fiber array and a wire-bonded printed circuit board (PCB) to make the module stable and compact. By simply adjusting the low-frequency electrical LO, the down converter based on FWM can realize accurate tunable and ultra-wide frequency operation. Due to the strengths of silicon integrated waveguide doped with reverse-biased P-i-N junction, the high-order LO modulated optical sidebands can be generated and used to down-conversion high-frequency RF microwave signal. This scheme can significantly reduce the high-frequency demand for LO source. In the experiment, the RF signals ranging from 8 GHz to 31 GHz are all down converted within 2 GHz by utilizing the 5.8 – 8.2 GHz LO signals, and signal-to-noise ratios (SNRs) larger than 50 dB are achieved. Moreover, the phase noise of the intermediate frequency (IF) signal is as low as -80.12 dBc/Hz at an offset frequency of 10 kHz and spurious free dynamic range (SFDR) is 105.5 dB · Hz ^2/3 with 3 ^rd -order FWM effect for the LO signal and 103.8 dB · Hz ^2/3 with 4 ^th -order FWM effect for the LO signal. This shows that the down conversion signal is reliable to further use in modern electrical systems such as microwave photonic radar.

Optical non-reciprocity is a significant property in numerous applications, ranging from optical telecommunications and optical signal processing to integrated photonics and quantum networks. Here, we theoretically demonstrate passive optical non-reciprocity with multiple modes in the visible range, employing a simple hybrid plasmonic nanostructure, which consists of a metallic cavity waveguide with two groups of gratings on both sides (ports). This structure illustrates high isolation ratios for these modes with values of around 10–30 dB. The maximum isolation ratio is close to 30 dB at the wavelength of 548 nm with the bandwidth of 16 nm. Furthermore, the intensity of the electric field localized inside the waveguide is highly enhanced by about 1 order of magnitude for these resonant modes. Our work presents a novel way for realizing optical non-reciprocity with multiple modes in the visible range, which is helpful forassociated applications.