Multiwavelength DFB laser array transmitters for ONTC reconfigurable optical network testbed

A 16-channel electroabsorption modulated tunable multi-wavelength DFB laser array is proposed and experimentally demonstrated. The sixteen DFB lasers, each with a wavelength spacing of 100 GHz, are arranged in a 4 × 4 matrix. The wavelengths are designed using an interleaving scheme to reduce grating crosstalk. The grating is designed and fabricated using the reconstruction equivalent chirp (REC) technique to simplify the grating fabrication and ensure precise wavelength control. The electroabsorption modulator and the tunable multi-wavelength laser array share the same active layer to reduce fabrication complexity and costs. Wavelength tuning is achieved by selecting the active laser without altering the thermoelectric cooler (TEC). Consequently, 16 channels with 100 GHz spacing are obtained, each operating in good single-mode properties with SMSRs of above 45 dB. The average wavelength spacing is 106.1 GHz, and only 6.1 GHz deviated from the design. The semiconductor optical amplifier (SOA) is integrated to compensate for the frequency chirp and amplify the output power, thus enabling long-distance transmission. The output power is amplified to over 18 mW with a 150 mA current injected into the SOA. The 3-dB bandwidth of the EAM exceeds 20 GHz, producing clear 25 Gb/s back-to-back eye diagrams with mask margins over 40% for the 16 channels. With the assistance of the chirp compensation by the SOA, the eye diagrams of the 16 channels remain clear after 10 km of transmission. Due to the superior performance, the proposed device is promising for use in DWDM systems, particularly in applications requiring fast channel switching, such as optical packet switching and NG-PON2 technology.

A multi-wavelength laser source is important for applications in areas such as wavelength-division multiplexing (WDM), interferometry, lidar and optical data storage. Simultaneous oscillation of multipe wavelengths have been demonstrated in several methods including spatially chirped Bragg reflector vertical cavity surface emitting laser (VCSEL) arrays,1 multichannel grating cavity (MGC) laser,2 multistripe array grating integrated (MAGIC) laser,3 and multi-wavelength DFB laser array by control selective area MOVPE.4 In those devices, arrays are required for the generation of multi-wavelength oscillation. Each array element is responsible for its individual wavelength oscillation. In this work, it is demonstrated that a single-stripe Fabry-Perot laser diode is able to oscillate at selected multiple wavelengths with a wavelength separation ≥1.3 nm, several times larger than the Fabry-Perot longitudinal mode spacing.

We have witnessed a rapid advancement in optical fiber telecommunications in the last decade. The bit rate of early optical transmission systems in the late 1970's was 45 Mbit/s. By the m1d4980's, the transmission speed had been increased to rates ranging from 400 Mbitls to 560Mbit/s. More recently, SONET hierarchy, from OC- 1 , OC-3, OC-12, to OC-48 at 51.84 Mbitis, 1 55.52MbitJs, 622 Mbitls to 2.488 Gbitls respectively, has been the standard chosen by CCITT. The next SONET standard rate of OC-l92 at 10 Gbitis is now under consideration. Although laser transmitters at 10 Gbitls rate are still in the research and development stage, new products will be introduced in the marketplace to fuffill systems and networking needs in the near future. The singlemode optical fiber has a potential bandwidth of over 30 THz. In order to utilize this bandwidth, high density wavelength-division-multiplexing (WDM) has been considered. WDM can offer not only the increased usage of bandwidth, but also the flexibility of routing signals in a network by means of wavelength [11. In the last few years, the transmission distances have been increased dramatically due to the use of Er-doped fiber amplifiers. High power semiconductor lasers at either 0.98 tm or 1.48 .tm wavelengths are used for the pump. The powers into the amplifier required for both pump wavelengths are about 20 mW and 50 mW respectively. On the other hand, semiconductor opticai amplifiers are attractive for monolithic integration with lasers, waveguides, modulators, wavelength multiplexers and demultiplexers. For example multi-wavelength DFB laser arrays, as many as 20 wavelengths, have been integrated monolithically with wavelength combiners (star coupler) and optical amplifiers on InP substrate [2). These integrated multi-wavelengths DFB laser arrays have the advantage of easier wavelength control and lower cost per wavelength than the discrete DFB laser transmitters for WDM applications. Such photonic integrated circuits (PlC) can increase the functionality and reduce the optical fiber-to-device interfaces that are the main factor for the high cost of optoelect.ronic components. The fiber-to-device interface is also the major concern for component reliability.

We review the progress of multiwavelength DFB laser arrays made for multiwavelength optical networks. The goal is to reduce the per-wavelength transmitter cost in manufacturing and network element control. Using photonic integration, we have addressed and resolved several important issues related to laser arrays such as wavelength accuracy, output power and optical packaging. State of the art results are summarized and its impact on the multiwavelength optical network is assessed.

A DFB semiconductor laser with a bent waveguide and an equivalent chirp compensation based on the sampled grating technique is proposed to improve the single longitudinal mode (SLM) performance for the first time. In such a structure, the bent waveguide is used to form the basically chirped grating so that the zeroth-order resonance is greatly suppressed. However, for the $-$ first-order resonance, the equivalent chirp by designing the sampling pattern is used to compensate the chirp in the $-$ first subgrating caused by bent waveguide. As a result, the $-$ first-order resonance is enhanced, whereas the zeroth resonance is well suppressed. Since the wavelength spacing between the zeroth and $-$ first subgrating can be reduced by adopting this method, the sampling period can be increased. Therefore, the corresponding line in photomask can be enlarged as well to ease the fabrication, and the lasing wavelength accuracy can be further improved according to the theoretical analysis. Because the lasing wavelength can be controlled by changing the sampling period, the performances of the multiwavelength DFB laser array can also be improved using this method.

An equivalent corrugation pitch modulated distributed-feedback semiconductor multiwavelength laser array (MLA) with two equivalently assisted phase shifts (EAPSs) based on the reconstruction-equivalent-chirp technique is theoretically studied and experimentally demonstrated. The simulated results show that the longitudinal photon density distribution of the studied MLA is much more uniform than that of the MLA without EAPSs. Accordingly, the longitudinal spatial hole burning of the proposed MLA is therefore suppressed more effectively. The experimental results show that the studied MLA has good single-longitudinal-mode performance. The highest side mode suppression ratio (SMSR) is even up to 52.63dB. Meanwhile, the tunable wavelength range of the investigated MLA is 25.94nm under the thermal tuning scheme from 15.12°C to 46.93°C. All channels are within a wavelength deviation of ±0.001n m. The SMSRs are all above 38dB.

A 12-channel 100-GHz-spacing thermally tunable multi-wavelength DFB laser array is demonstrated based on reconstruction-equivalent-chirp technique with good single-longitudinal-mode property (SMSR > 50 dB) and small temperature tuning range (15.5 °C).

We discuss the advantages of wavelength-division-multiplexed (WDM) lightwave systems and the need for monolithically integrated multiwavelength laser arrays. For WDM light-wave systems to be cost effective, it is important to reduce the per-wavelength component cost. By photonic integration, the packaging and the control circuitry will be shared among all the wavelengths. In this paper, we review the multiwavelength laser arrays, the array coupling, and the photonic integration approach. We have demonstrated the monolithic integration of a 21-wavelength multi-quantum-well distributed-feedback laser array with a star coupler and optical amplifiers on the same chip. Operating a packaged module under CW operation, we obtained as many as 15 individual wavelengths simultaneously launched from one output port of the star coupler of this integrated chip into one lensed single-mode fiber. We also characterized the thermal and the electrical crosstalk from the neighboring lasers. This integrated chip stands a good chance of being a compact and low-cost multiwavelength laser source for future WDM lightwave systems.

We propose what we believe to be a novel method for realizing monolithically integrated multi-wavelength surface-emitting laser arrays (MWSELAs) and experimentally demonstrate its feasibility. The MWSELA consists of six oxide-confined grating-coupled surface-emitting lasers (GCSELs), where the emission wavelength of each device is tuned by adjusting the period of the surface grating while maintaining an identical epitaxial structure. The fabricated six-wavelength GCSEL array achieves precise wavelength control with an average wavelength spacing of 1.6 nm. All elements in the array exhibit excellent single-mode operation, with side-mode suppression ratios exceeding 30 dB at an injection current of 12 mA and low threshold currents of approximately 1.5 mA. The proposed method offers a new pathway to realize monolithically integrated MWSELAs with flexible physical layouts through a simplified fabrication process. Its advantages-including low power consumption, stable single-mode performance, and compatibility with wafer-level manufacturing and testing-make it an ideal candidate for developing cost-effective MWSELAs.

With the significant technology advancement in photonic integration and the demands of compact light sources of multiple wavelengths, multiwavelength laser arrays (MWLAs) can play important roles in high-capacity optical signal transmission, photonic switching, and optical sensing. Manufacturing with semiconductor foundries and the integration with electronic integrated circuits bring not only advanced technologies but also new concepts for realizing MWLAs. This paper will first overview the existing technology development and then discuss the challenges and possible solutions for enabling photonic-integrated MWLAs. The overview will cover monolithically and hybrid-integrated MWLAs. The wavelength registration for both in-plane and vertical-cavity MWLAs will be discussed and compared.

We present a novel multiwavelength laser array with a sampled grating formed by periodically loaded n-doped injection blocking layer on top of the uniform base grating. With an optimized design of the sampled grating as well as the laser operation conditions, all the even order, including the zeroth-order reflections, can be effectively suppressed, leaving only the first-order reflection wavelength to lase. Unlike in the conventional sampled grating where part of the base grating will have to be removed, the whole base grating is retained in the proposed structure; hence, the side-mode suppression ratio will not be jeopardized due to the weakened grating coupling strength. As an example, an array of 12 lasers has been designed to cover a wavelength range from 1542 to 1560 nm.

Integrated dissipative Kerr soliton optical frequency comb has been recognized as a promising on-chip multi-wavelength laser source for fiber optical communications, as its comb lines possess frequency and phase stability far beyond the independent lasers. In the scenario of coherent optical transmission and interconnect, a highly beneficial but rarely explored target is to re-generate a Kerr soliton microcomb at the receiver side as local oscillators that conserve the frequency and phase property of the incoming data carriers, so that to enable coherent detection with minimized optical and electrical compensations. Also, in the scenarios of all-optical signal regeneration, a multi-wavelength coherent laser array is also needed to provide the coherent pump fields that enable phase-sensitive parametric amplification of the degraded data signals and constitute regenerative phase transfer functions. In this talk, we will introduce our recent experiments that implement re-generation of a Kerr soliton microcomb that faithfully clones the frequency and phase coherence of another microcomb. We show that such coherence-cloned carrier and LO microcombs can greatly facilitate coherent data receiving by making DSP-based compensations for carrier-LO frequency offsets and phase drifts substantially easier, and at most 1000 times more energy-saving, comparing with a system adopting individual laser carriers and LOs. Moreover, we will also discuss that the coherence-cloned Kerr microcombs can be used to implement multi-channel, configurable all-optical signal regeneration in nonlinear silicon waveguide, phase regenerations of two channel BPSK signals are demonstrated with prominent signal quality improvements. Our work reveals that, in addition to providing a multitude of laser tones, regulating the frequency and phase of Kerr soliton microcombs among data transmitters, regenerators, receivers within an optical network can significantly improve the network performance in terms of signal quality, power consumption, and simplicity.

Summary form only given. A novel scheme of laser spectroscopy is proposed and demonstrated based on a multi-wavelength dye laser array chip without wavelength scanning. An example is shown of the novel application, where the multi-wavelength output from the waveguided DFB dye laser is used which can be realized by fabricating a DFB structure with different wavelength on each waveguide. Generally the laser wavelength has to be scanned for the spectral analysis application. On the other hand, the proposed scheme with an all-solid-state polymer laser realizes a very fast and digital spectrum analysis without any spectral scan. Since the wavelengths of the waveguides can be programmed as needed, even a nonlinear spectral profile is also possible. A copolymer with rhodamine 6G was used as a core layer of the waveguide. For spectroscopy application, fifteen DFB waveguides were fabricated with a spectral pitch of 0.11 nm in the spectral region from 589.4 nm to 591.0 nm, which can cover the primary absorption D lines of sodium atom. The measurement of D lines using the multi-wavelength DFB dye laser integrated on a single chip has been demonstrated.

A method used to introduce an arbitrary equivalent-phase-shift (EPS) into an asymmetric sampled Bragg grating (SBG) is reported. Under the same structural parameters except for the sampling pattern, the asymmetric SBG offers better performance than that of a normal SBG structure for keeping single-longitudinal-mode (SLM) operation. This is because the proposed sampling pattern can suppress the 0th-order light resonance due to the mismatch between the two different grating sections along the whole SBG. This method can be used to design and fabricate semiconductor lasers and multiwavelength laser arrays (MLAs) with the required EPS at high yield and low cost.

The multiwavelength laser array (MLA) with fine wavelength tunability is demonstrated experimentally. The studied MLA has good single-longitudinal-mode performance, and the side-mode suppression ratio (SMSR) even reaches 62.1 dB. Meanwhile, the wavelength range of the MLA can be tuned to 25.003 nm with 63 channels of 50 GHz spacing. All lasers are within a wavelength deviation of ±0.02nm. The output power is almost constant with standard deviation 0.63 dBm. The SMSRs are all above 50 dB.