All-optical switches have the advantage of significantly reducing the cost of data-center and improving the transmission characteristics of the system, which has led to many different optical switching technologies for data-center. For this application, we demonstrate a superfast wavelength switching drive design for DFB laser array, and realize a fast tunable laser with 5 ns switching latency. The laser array (C-band, 16-channel, 100 G-space) we used is based on the reconstructed equivalent chirp technology. During the process of tuning, the output wavelength of each channel is within the channel wavelength error range specified by DWDM under the ITU-T standard. Based on the above light source, we build a complete prototype of all-optical switching transceiver integrating transceiver and transmitter, and demonstrate the stable transmission of 10.24 Gb/s data under the condition of four wavelength arbitrary switching and routing.
Photodetectors (PDs) are optoelectronic (O/E) devices to achieve optical-to-electrical conversion, which are essential and of great importance in optical communication, optoelectronic oscillator, etc. Measuring O/E frequency responses, including magnitude response and phase response, is a fundamental measurement processing in their development and application. Microwave photonics (MWP) is a promising solution to achieve ultrahigh-resolution characterization. However, the frequency measurement range is restricted by the relatively small working bandwidth of modulators. To enlarge the measurement range, an approach to measure magnitude response of O/E devices is proposed and experimentally presented. In the approach, two optical double-sideband (ODSB) signals with the carrier suppression are generated. One ODSB signal filtered out +1st-order sideband is used as the frequency-shifted carrier. By coupling the frequency-shifted carrier and the other ODSB signal, an asymmetrical ODSB signal is thus achieved and served as a probe signal. After square-law detection of a PD under test, a photocurrent is produced. Detecting the frequency downconversion component in the produced photocurrent, the magnitude response in the low-frequency regime is obtained. Similarly, the magnitude response in the high-frequency regime is observed via extracting the magnitude information of the frequency up-conversion component. Thanks to the MWP-based frequency conversion, the measurement range is doubled, and the nonlinear error is suppressed. Furthermore, an ultrahigh-frequency resolution up to Hz or even sub-Hz is theoretically achievable. In an experiment, a 20-GHz commercial PD is accurately measured using a 200-kHz resolution. A measurement range as large as 67 GHz is enabled by 33.5 GHz RF frequency sweeping.
As a key component of all-optical switching network terminal technology, ultra-fast wavelength-tunable laser arrays are critical to the high integration and performance improvement of the entire optical switching system. In this article, the array of 2×8 matrix grating DFB laser arrays that we used are based on reconstruction equivalent chirp technology. The wavelength range is in the C-band. Based on this, we designed an excellent control circuit and a high-speed drive circuit for the needs of the laser array to provide the laser array with a drive current that can control the ultra-high-speed switching of channels. The final experimental results show that the channel spacing of the 16 channels of the laser array is 100G, In addition, the switching time of any two channels is less than 10 nanoseconds, and the wavelength selection time has nothing to do with the wavelength range. During the switching process, the centre wavelength drift of each channel is always within the channel wavelength error specified by WDM under the ITU-T standard.
This paper introduces the influence of the frequency response of the optical eye diagram analyzer on the test results, and the common methods of the frequency response calibration of the optical eye diagram analyzer. The principle of using femtosecond laser to calibrate the filter frequency response of the optical eye diagram analyzer is analyzed. The femtosecond laser is approximated to the impact function, and the impulse response of the filter can be obtained. The frequency response of the filter is calculated by Fourier transform. A scheme of calibrating filter frequency response of optical eye diagram analyzer with femtosecond laser is proposed. The pulse width and repetition frequency of femtosecond laser are tested. The influence of the stability of femtosecond laser repetition frequency on the test results is analyzed. At the same time, this paper introduces the test results of the frequency response of calibrating the optical eye diagram analyzer by the optical heterodyne method, and comparatively analyzes the optical heterodyne method and the femtosecond laser method. The experimental results show that it is feasible to calibrate the frequency response of the photoelectric module of Oscilloscope by femtosecond laser, and the repeatability of 3dB bandwidth is less than 6%.
In this paper, a series of research on the stable output method of Mach-Zehnder frequency domain depolarization system is carried out. Based on the analysis of Mach-Zehnder frequency domain depolarization technology and DOP measurement technology, it is pointed out that the instability of DOP of the depolarization system has an adverse effect on the calibration of the DOP meter with the extremum search method. It is clear that the instability problem is mainly due to the accurate alignment deviation of optical fiber. As a result, a set of solutions to improve the stability is proposed and verified by experiments. The technical core of this scheme is to extend the SOP of the depolarization system from half range control to full range control, reduce the correlation between SOP control and power control, and overcome the problem of optical fiber axis deviation in conventional technology. Through the experimental verification, the Mach-Zehnder frequency domain depolarization system based on the scheme proposed in this paper can effectively control the stability of the DOP of the output light within ± 0.1%, which can effectively calibrate the DOP meter with the extremum search method.
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