KEYWORDS: All optical switching, Optical switching, Tunable lasers, Field programmable gate arrays, Ultrafast phenomena, Modulation, Switching, Eye, Data transmission, Temperature control
The all-optical switching system can effectively solve problems such as transmission delay and bottleneck bandwidth. And it has significant advantages in reducing data center costs and improving its transmission characteristics. The basic idea of this study is to achieve ultra-low power consumption, ultra-low latency, and ultra-low cost switching networks through the all-optical switching system. Due to the advantages of high bandwidth and low loss, all-optical switching system are expected to replace the existing electric switching communication network in Data Center. For this system, we produced a fast tunable laser array (C-band, 16-channel, 100 GHz-space) with a switching delay of 5 ns. Each wavelength is within the error range of the channel wavelength stipulated by the Dense Wavelength Division Multiplexing (DWDM) under the ITU-T channel standard during tuning. Based on the above-mentioned laser sources, the drive control unit of the array-type tunable DFB laser was prepared, and a DWDM all-optical switching system test bed with an arrayed waveguide grating router as the core was built. Define the above laser, drive control unit and modulator as a node that can achieve arbitrary routing in the all-optical switching system mentioned above through wavelength control. A stable data switching and transmission of 20.48 Gb/s is demonstrated, in which four nodes with four different wavelengths are adopted, and full cross routes are realized.
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.
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.
Wavelength-swept laser is one of the most critical common components of fiber Bragg grating (FBG) sensors. However, a fast, stable, integrated and low-cost multi-channel wavelength-swept laser array is still unavailable. In this article, a multi-channel simultaneous wavelength-swept DFB laser array based on the reconstruction-equivalent-chirp (REC) technique is proposed and manufactured. The REC technology simplifies the fabrication process and greatly reduces the cost of the laser. The laser array contains 4 lasers in parallel with integrated heating resistance for thermal tuning to broaden the wavelength-tuning range. Each single-wavelength DFB laser introduces a π-phase shift structure, which is used to improve the single-mode performance of the laser. Meanwhile, the active multiplexer responsible for coupling and an optical amplifier (SOA) responsible for compensating the coupling loss of the laser are also integrated on the same chip. The driving circuits of the laser use FPGA to control the DAC chip to obtain precise current output and realizes continuous linear output of wavelength by changing the injection current size. The packaged laser module can realize a continuous wavelength-swept range of 2.4 nm per channel with the SMSR over 40 dB, achieving a simultaneous sweep of four channels with good scanning linearity and scanning speed. The work of this paper realizes the integration of linear wavelength-swept light sources, which creates the conditions for a low-cost, small-volume multi-channel sensing system in the future.
Fast tunable lasers with switching time less than one microsecond are key components in high-speed optical switching networks. In this paper, we propose an effective method to achieve high wavelength switching speed by turning on/off individual lasers of a matrix-grating DFB laser array. The laser array consists of 16 DFB lasers, which are arranged as a 4-by-4 matrix. Besides, the REC technique is used to simplify the fabrication of the grating and precisely control the grating phase. 16 channels with 2.4-nm-spacing are obtained and the SMSRs of all the 16 channels are above 40 dB, indicating good single mode operation. A high-speed driving circuit is designed to supply stable direct current for the DFB laser array and to control the switching process. The experimental result shows that the switching time between 2 channels is less than 100 nanoseconds.
We propose and fabricate a linear frequency-swept DFB laser array based on the reconstructed-equivalent-chirp (REC) technique used in sensing system. During the fabrication process of the laser arrays, the reconstructed-equivalent-chirp technique is utilized to simplify the fabrication of the grating and precisely control the grating phase. A semiconductor optical amplifier (SOA) is monolithically integrated to enhance and balance the output optical power. The module achieves a wavelength range of more than 3 nm by covering 4 channels with an interval of 0.8 nm. The side mode suppression ratios (SMSRs) of all channels are above 50 dB and the output power are guaranteed above 10 dBm with the SOA providing 14 dBm saturation output power. To tune the wavelength on the microsecond scale, we adopt a combination of a MCU and a FPGA as the controlling core to turn on and off the driving current of all the 4 lasers on the DFB laser array, and the switching time between 2 channels is well controlled within 50 ns. At the same time, the module makes the wavelength output linearly with the current through the filter circuit, and achieves the sweep speed of 100 nm/s. This sweep speed, sweep range, output power, and good single-model performance meet the needs of sensing system for light sources.
KEYWORDS: Switching, Semiconductor lasers, Field programmable gate arrays, Switches, Fabrication, Analog electronics, Transform theory, Digital electronics, Feedback control, Time metrology
We propose and fabricate a rapidly wavelength switching DFB laser array based on Reconstructed-Equivalent-Chirp technique. A Semiconductor Optical Amplifier(SOA) is applied to enhance and balance the output optical power. The module covers 8 channels from 1554.5nm to 1566.1nm with an interval of 1.6nm. To tune the wavelength on the microsecond scale, we adopt a combination of a MCU and a FPGA as the controlling core to turn on and off the driving current of 8 lasers on the DFB laser array through a collector feedback circuit, and the switching time between 2 channels is well controlled within 300ns. The side mode suppression ratios(SMSRs) of all channels are above 50dB and the output power are guaranteed above 10dBm with the SOA providing 14dBm saturation output power.
A wavelength-tunable small form-factor pluggable (SFP) optical module is proposed and implemented, which is based on a self-designed 4-channel DFB laser array. The module adopts the widely used SFP packaging standard so that it is convenient to connect with other devices. It has an I2C interface for receiving wavelength tuning commands and downloading digital diagnostics monitoring information to the host processor. Three parts are included: the receiver, the transmitter and the microcontroller unit, to complete the conversion of optical-electro, electro-optical. A large range and high precision wavelength tuning is realized through innovative tuning methods. Two wavelength tuning methods are utilized: channel switching of 4-channel for coarse tuning and temperature tuning combined with current tuning for fine tuning to actualize the tunable output of the DFB laser array. This wavelength-tunable SFP optical module can replace several fixed wavelength optical modules in a traditional WDM system, thus greatly reducing costs and improving the utilization ratio of resources. Experimental results show the SFP optical module can achieve the continuity of wavelength tuning covering 1539.0 nm to 1551.0 nm. It can switch over 16 channels in a 100G-DWDM system or 31 channels in a 50G-DWDM system. The side mode suppression ratios (SMSRs) of most channels are above 40dB over the wavelength tuning range of 12 nm. The optical signal transmission rate is up to 1.25Gbps.
We propose a new method to investigate fast wavelength switching, which consists of control circuit, driving circuit and 8-channel DFB laser array using reconstruction-equivalent-chirp technique. The control circuit is in charge of selecting required lasers to switch wavelength, the driving circuit supply adjustable and stable direct current to the DFB laser arrays. Experimental results show that wavelength switching time of 8 channels is about 500ns and stability of laser output is promised.
An innovative approach to realise high chip rate in OCDMA transmission system is proposed and experimentally investigation, the high chip rate is achieved through a 2-D wavelength-hopping time-spreading en/decoder based on the supercontinuum light source. The source used in the experiment is generated by high nonlinear optical fiber (HNLF), Erbium-doped fiber amplifier (EDFA) which output power is 26 dBm, and distributed feed-back laser diode which works in the gain switch state. The span and the flatness of the light source are 20 nm and 3 dB, respectively, after equalization of wavelength selective switch (WSS). The wavelength-hopping time-spreading coder can be changed 20 nm in the wavelength and 400 ps in the time, is consist of WSS and delay lines. Therefore, the experimental results show that the chip rate can achieve 500 Gchip/s, in the case of 2.5 Gbit/s, while keeping a bit error rate below forward error correction limit after 40 km transmission.
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