A Tunable Multiwavelength Laser Employing a Semiconductor Optical Amplifier and an Opto-VLSI Processor

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.

Band-gap shrinkage is an important effect in semiconductor lasers and optical amplifiers. In the former it leads to an increase in the lasing wavelength and in the latter an increase in the gain peak wavelength as the bias current is increased. The most common model used for carrier-density dependent band-gap shrinkage is a cube root dependency on carrier density, which is strictly only true for high carrier densities and low temperatures. This simple model, involves a material constant which is treated as a fitting parameter. Strained InGaAsP material is commonly used to fabricate polarization insensitive semiconductor optical amplifiers (SOAs). Most mathematical models for SOAs use the cube root bandgap shrinkage model. However, because SOAs are often operated over a wide range of drive currents and input optical powers leading to large variations in carrier density along the amplifier length, for improved model accuracy it is preferable to use band-gap shrinkage calculated from knowledge of the material bandstructure. In this letter the carrier density dependent band-gap shrinkage for strained InGaAsP is calculated by using detailed non-parabolic conduction and valence band models. The shrinkage dependency on temperature and both tensile and compressive strain is investigated and compared to the cube root model, for which it shows significant deviation. A simple power model, showing an almost square-root dependency, is derived for carrier densities in the range usually encountered in InGaAsP laser diodes and SOAs.

A narrow linewidth electro-optically tuned multi-channel interference (MCI) widely tunable semiconductor laser based on carrier injection is demonstrated in this paper. The MCI laser with a common phase section and a semiconductor optical amplifier (SOA) is packaged into a 16-pin butterfly box. The laser is characterized by a strategy: shifting the longitudinal mode and then aligning the reflection peak, which obtains a quasi-continuous tuning range over 48 nm. The corresponding side mode suppression ratios (SMSRs) are higher than 40 dB and frequency deviations from ITU-grid are less than ± 1 GHz. Threshold currents are less than 28 mA. Fiber coupled output powers are higher than 20 mW and power variations with fixed gain and SOA currents are less than 0.8 dB over the whole tuning range. Lorentzian linewidths are less than 320 kHz over the entire tuning range, which is one of the lowest results for monolithic widely tunable semiconductor lasers tuned by carrier injection. These results demonstrate the potential prospects of the MCI laser with carrier injection in the field of optical sensing and optical communications.

We demonstrate a tunable narrow-linewidth laser based on a semiconductor optical amplifier and a linearly chirped FBG. High tuning resolution and small power variation over 40 nm tuning range were achieved by optimizing the drive current. © 2019 The Author(s)

Future high capacity wavelength division multiplexed (WDM) optical networks will rely on transmitting signals with information encoded on both the amplitude and phase of multiple optical carriers. To optimise the efficiency of these networks, they are likely to employ some level of wavelength switching [1], and a key function required by wavelength switching is wavelength conversion [1]. Wavelength conversion of phase modulated signals in wavelength switched optical networks will need to be undertaken using a coherent nonlinear process, such as four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) [2] employing a fast wavelength tuneable pump laser to ensure an optical channel can be dynamically routed to different wavelengths. A crucial issue that is likely to have a major impact on the wavelength conversion of such high capacity signals using FWM is the phase noise transfer to the converted signal. A detailed study of FWM wavelength converted continuous-wave signals in [3] showed that the phase noise transfer from the pump to the idler, increased the linewidth of the idler by a factor of 4 relative to the pump. Such a large line broadening is highly detrimental to the detection of phase-encoded signals, especially since the tuneable lasers that exhibit small wavelength switching times (<;50 ns) and would be employed in wavelength switched networks tend to have linewidths of the order of a few MHz [4]. Therefore estimating the linewidth limits that enable FWM wavelength conversion using this scheme is vital to select a tuneable pump laser with suitable linewidth.

To enhance the functionality and flexibility of a multiwavelength fiber laser, characteristics such as the tunability of the lasing wavelength, the wavelength spacing and the number of channels should be investigated simultaneously. We have demonstrated a channel spacing and wavelength tunable multiwavelength fiber ring laser based on semiconductor optical amplifier and a novel tunable polarization-diversity loop configuration (PDLC)-based comb filter. The tunable PDLC-based comb filter would be composed of a polarization beam splitter and three wave plates (one quarter wave plate and two half wave plates) and a polarization differential delay line (DDL). Channel spacing can be controlled continuously by using a motorized polarization differential delay line. And wavelength can be simultaneously changed by controlling wave plates. The PDLC-based comb filter has the advantages of the input polarization independence and simple tunability. By employing the comb filter in the laser system, multiwavelength operation of up to 25 laser lines with the signal-to-noise ratio over 25 dB and 0.8 nm wavelength spacing has been demonstrated at room temperature. Also, we could achieve the increased output channel power of the laser while reducing the number of channels. The results show that the multiwavelength operation is even and stable. And we could achieve the output spectra of tuned wavebands with channel spacing of 1.6 nm and 0.4 nm when the semiconductor optical amplifier is driven with the injection current of 160 mA while adjusting a half-wave plate at each tuning set. As a result, the shift of lasing wavelength and wavelength spacing were continuously controllable in this system.

A multi-wavelength laser source is demonstrated with a semiconductor optical amplifier (SOA) as a gain medium. A multi-wavelength comb with equal spacing is achieved due to Fabry–Pérot modes of the SOA which oscillates in the ring cavity. A 100 m long photonics crystal fiber (PCF) is inserted in the ring cavity to provide a nonlinear gain by four-wave mixing (FWM) so that the output comb spectrum can be greatly broadened and flattened. The stability of the ring laser is also increased due to the efficient FWM phenomenon occurring in the PCF. The SOA-based laser can generate 35 lasing lines with equal spacing of 0.28 nm and extinction ratios of more than 30 dB at room temperature. The number of channels of the multi-wavelength laser can be controlled flexibly by changing the ratio of the coupler used in the ring cavity configuration as well as controlling the polarization state of the oscillating laser.

Summary form only given. An overview is presented of the progress in design and characteristics of semiconductor optical amplifiers (SOA) for 1310, 1400 and 1550 nm operation in fiber optical transmission systems. The technology and performance of SOAs will be discussed with respect to optical gain, noise figure, saturation output power and polarization (in-) dependent behavior. The use of both strained quantum wells and bulk tensile material will be discussed in view of obtaining polarization independent behavior. Gain clamping in SOAs has been shown to improve the linearity performance especially for analogue signal transmission. The SOA technology has been demonstrated for optical pre-amplification, in-line application and optical booster applications. DWDM experiments using SOAs in up to 20 Gbit/s systems in short- and medium-distance transmission will be highlighted. Also, SOAs have been used in optical demultiplexing from 40 Gbit/s down to 10 Gbit/s RZ signals using its phase properties and in integrated photonic devices like multiwavelength lasers.

A recently reported theory of gain recovery in semiconductor optical amplifiers (SOAs) is extended to develop approximate expressions for the gain compression and recovery time in terms of probe wavelength, unsaturated gain and device length. These results indicate (1) that the gain recovery time should be approximately inversely proportional to the transmission gain spectrum, and (2) that the wavelength dependence of the gain compression caused by the pump pulse will be dominated by the spectrum of the SOA gain at the probe wavelength. These predictions are tested against pump-probe measurements of gain compression and recovery in a series of four semiconductor optical amplifiers of different lengths but otherwise identical structures. A continuous wave probe beam from a tunable laser is used to measure the wavelength dependence of gain compression and recovery times. Spectral features are used to verify the correlations between these quantities and their dependence on device length.

In this paper, we have proposed and demonstrated a multi-wavelength laser source based on a semiconductor optical amplifier (SOA) and optical filter module. The optical filter module is composed from a polarizer (P), polarization controller (PC), polarization maintaining fiber (PMF) and mirror. The multi-wavelength laser is generated by constructing SOA and optical filter module in a loop. The output wavelengths are determined by an optical filter module. The Experimental results revealed that a stable multi-wavelength lasing with 0.27 nm wavelength spacing is achieved at room temperature. Moreover, the proposed method is cost effective compared to the previously proposed schemes.

A theoretical model is presented to analyze the noise suppression characteristics in cross-gain-compression (XGC)-based regenerators, where an optical bandpass filter (BPF) is cascaded after a semiconductor optical amplifier (SOA). Analytical expressions of variance are obtained for in-phase and quadrature noises after SOA and after filter. The result shows that the physical mechanism behind XGC-based noise suppression is that gain change in the SOA is out of phase with the input power fluctuation, which leads to a negative cross-correlation term in the expression of in-phase noise variance at SOA output. On the other hand, nonlinear phase noise introduced by refractive index change in the SOA will contributes to quadrature noise, which is proportional to the square of the linewidth enhancement factor ~ αN2. It is proposed that a slightly blue-shifted optical BPF can convert phase/quadrature noise-related frequency chirp into amplitude fluctuation that can cancel a part of the amplitude fluctuation after SOA, thus lead to further reduction of in-phase noise. This mechanism can be used to alleviate the negative effect of SOA-induced nonlinear phase noise and enhance the overall noise suppression performance of XGC-based regenerators, which is experimentally and numerically demonstrated at 10 Gbit/s.

A multi-wavelength tunable fiber laser is constructed for a wavelength-division multiplexed (WDM) fiber Bragg grating (FBG) sensor array in which simultaneous detection of multipoint vibrations and temperature stabilization of the sensor outputs are achieved. The laser consists of a semiconductor optical amplifier (SOA) as a gain medium and of FBGs as wavelength selection components. Since the SOA is an inhomogeneous broadening gain medium, stable multi-wavelength oscillation at the Bragg wavelengths of the FBGs can be realized. In addition, the oscillation wavelengths of the laser can be tuned by applying strain to the FBGs used. In the sensor scheme, triple wavelength fiber laser is fabricated, in which the three wavelength components provide narrowband light sources for arrayed WDM FBG sensors and the wavelength tuning enables temperature compensation for the vibration detection. In the experiment, simultaneous three-point vibration detection with temperature stabilization has been successfully demonstrated.

In this paper, the development of loop mirror multi-wavelength Brillouin fiber laser utilizing semiconductor optical amplifier and fiber Bragg grating is successfully demonstrated. A multi-wavelength BFL structure employs a single mode fiber that acts as the gain medium, while the fiber Bragg grating act to reflect the signals and semiconductor optical amplifier is used to amplify the signal are employed to produce multiple channels. The implementation of difference parameter for semiconductor optical amplifier driven current, Brillouin pump power, Brillouin pump wavelength and length of single mode fiber, plays an important role in producing the multiple channels. The highest number of channels which is 15 achieved once 9 km of SMF length, semiconductor optical amplifier current at 800mA and low Brillouin pump power at -12 dBm are utilized in the laser structure. Furthermore, the implementation of semiconductor optical amplifier and reflectivity of fiber Bragg grating in Brillouin fiber laser structure gives a better performance in producing the multiple channels.

L-Band on-chip heterogeneous integration lasers and semiconductor optical amplifiers (SOA) are important silicon photonics components in many applications such as light detection and ranging (LiDAR) and optical communications in data center interconnects. In this work, we demonstrate an L-band widely tunable laser and a high gain SOA on a III-V/Si integration platform. The laser gives a tuning range of 43 nm with side-mode suppression ratio > 45 dB, and output power of 9.15 mW, while the SOA shows a small-signal gain of 21 dB and a saturation output power of 13 dBm. The SOA and laser share the same III-V epitaxial wafer structure and a common fabrication process, which benefits the high-density components integration and reduces costs greatly in many applications.

C-band continuously tunable lasers using tunable fiber Bragg gratings