Chirp Managed Laser Research Articles

Modulator-Free Variable Multi-Rate FSO Communication 1 km Outfield Demonstration Based on Chirp-Managed Laser

Due to the high energy efficiency per bit and high sensitivity, Return-to-zero differential-phase-shift-keying (RZ-DPSK) is perfectly suitable for free-space laser communications. However, the conventional generation method of RZ-DPSK optical signal requires two modulators, which is costly, bulky, and heavy, significantly hindering the application of RZ-DPSK in size, weight, and power (SWaP)-constrained satellite platforms. In this paper, we propose and experimentally demonstrate a modulator-free variable multi-rate RZ-DPSK free-space optical (FSO) communication system based on chirp-managed laser (CML). Based on the proposed scheme, an FSO outfield experiment over 1 km has been successfully undertaken, achieving receiving sensitivities of −48.9 dBm and −45.6 dBm at 2.5 Gbps and 5 Gbps, with bit error rate (BER) of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> without forward error correction (FEC), respectively. The performance of the proposed system is also investigated by studying the eye diagrams under two different test conditions of back-to-back transmission and 1-km free space transmission. In addition to the small size, lightweight and low cost, the proposed scheme shows great potential for a variety of FSO communication applications ranging from Cube-Star to larger satellite laser communication platforms.

Multi-modulation compatible miniaturization system for FSO communication assisted by chirp-managed laser.

In recent years, the thriving satellite laser communication industry has been severely hindered by the limitations of incompatible modulation formats and restricted Size Weight and Power (SWaP). A multi-modulation compatible method serving for free-space optical (FSO) communication has been proposed assisted by chirp-managed laser (CML). The corresponding demonstration system has been established for realizing free-switching between intensity (OOK) and phase modulation (RZ-DPSK). The feasibility and performance of system have been evaluated sufficiently when loading with 2.5 and 5 Gbps data streams, respectively. Additionally, a control-group system has been operated utilizing Mach-Zehnder modulator (MZM) for comparison between CML-based and MZM-based compatibility solutions. The OOK receiving sensitivities of CML-based system are -47.02 dBm@2.5 Gbps and -46.12 dBm@5 Gbps at BER of 1×10-3 which are 0.62 dB and 1.11 dB higher than that of MZM; the receiving sensitivities of RZ-DPSK are -50.12 dBm@2.5 Gbps and -47.03 dBm@5 Gbps which are 0.79 dB and 0.47 dB higher than that of MZM respectively. Meanwhile, CML-based transmitter abandoned the traditional modulator and its complicated supporting devices which can effectively contribute to the reduction of SWaP. The CML-based system has been proven to have the compatibility between intensity and phase modulation while also possesses a miniaturized design. It may provide fresh thinking to achieve a practical miniaturization system for satisfying the requirements of space optical network in future.

Optimization design of chirp managed lasers by integral layer-peeling method

The chirp managed laser (CML) mainly includes a directly modulated laser followed by an optical spectrum reshaper (OSR) filter. In this paper, an integral layer-peeling method has been applied to synthesize the OSR filter with the desired reflection spectrum, which breaks the trade-off between the filter bandwidth and the filter slope steepness inherently existing in the FP etalon based filter, and hence greatly facilitates the optimization design of the OSR for a better transmission performance of a CML. Using this approach, we have, respectively, investigated the optimization design of the OSR filter in terms of the edge slope and the 3 dB bandwidth in the CML modulated at 10 and 25 Gb/s, through studying their transmission performances over the standard single-mode fiber. With the optimum design of OSR, the longest transmission distances at which the power penalty is 1 dB at a bit error rate of 10−12 are 135 and 18 km for the 10 and 25 Gb/s CML, respectively.

Monolithically integrated chirp-managed laser based on a resonant tunneling filter

We have proposed a monolithically integrated chirp-managed laser (CML) that consists of a directly modulated single-mode DFB laser and an optical spectrum reshaper (OSR) filter based on a double-slanted-trench resonant tunneling structure (DST-RTS). Slanted trenches facilitates the occurrence of resonant tunneling effect, which produces a steep-edge narrow-band OSR filter, and meanwhile directing most of the reflected waves out of the laser cavity, consequently eliminating the need of an isolator. Characteristics of the DST-RTS filter have been investigated and simulation results show that the proposed 25 Gbps 1.55 μm CML can send signal over 22 km standard single-mode fiber for bit error rate of 10−12.

Direct DPSK modulation of chirp-managed laser as cost-effective downstream transmitter for symmetrical 10-Gbit/s WDM PONs

This paper proposes the use of chirp-managed lasers (CML) as cost-effective downstream (DS) transmitters for next generation access networks. As the laser bandwidth is as high as 10 GHz, the CML could be directly modulated at 10 Gbit/s for downstream transmission in future wavelength division multiplexing passive optical networks (WDM PON). The laser adiabatic chirp, which is the main drawback limiting the transmission performance of directly modulated lasers, is now utilized to generate phase-shift keying (PSK) modulation format by direct modulation. At the user premise, the wavelength reuse technique based on reflective colorless upstream transmitter is applied. The optical network unit (ONU) reflects and orthogonally remodulates the received light with upstream data. A full-duplex transmission with symmetrical 10-Gbit/s bandwidth is demonstrated. Bit-error-rate measurement showed that optical power budgets of 29 dB at BER of 10(-9) or of 36 dB at BER of 10(-3) could be obtained with direct phase-shift-keying modulation of CML which proves that the proposed solution is a viable candidate for future WDM-PONs.

A novel symmetric 10 Gbit/s architecture with a single feeder fiber for WDM-PON based on chirp-managed laser

We propose the single feeder fiber architecture for wavelength division multiplexing passive optical network (WDM-PON) based on directly modulated chirp managed laser (CML). The downlink (DL) signal output from the laser is converted to return-to-zero (RZ) differential phase shift signal using a pulse carver. The downstream signal is reused as a carrier for the upstream using intensity modulation technique. Simulation results show the error-free performance at symmetric data rate of 10 Gbit/s per channel with negligible power penalty and improved receiver sensitivity for the uplink (UL), over 25 km standard single-mode fiber (SSMF). A low-cost and reduced circuitry network design is implemented on a single feeder fiber with the elimination of differential encoder and one external modulator.

Generation of Return-to-Zero Optical Pulses Using Directly Modulated Chirp Managed Laser

We propose and experimentally demonstrate the generation of return-to-zero (RZ) optical pulses with duty cycles of 33% and 67% using a directly modulated chirp managed laser (CML) driven by a sinusoidal signal at half pulse rate. No external pulse carver is required. The transmission performance of a 10-Gb/s RZ differential phase-shift keying (RZ-DPSK) signal based on CML pulses is also investigated. It shows comparable fiber chromatic dispersion tolerance and fiber nonlinearity robustness in single-channel test, compared with the conventional RZ-DPSK signal generated, via an external pulse carver.

Generation and Transmission of 10-Gb/s RZ-DPSK Signals Using a Directly Modulated Chirp-Managed Laser

We propose and experimentally demonstrate the generation of a 10-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) signal based on a directly modulated chirp-managed laser (CML), without requiring any differential encoder and optical phase modulator (PM). It shows better fiber chromatic dispersion tolerance and comparable nonlinearity tolerance, compared with a PM-based RZ-DPSK signal using 231 - 1 pseudorandom bit sequence data.

Chirp Managed Laser and Applications

The chirp managed laser (CML) is an alternative transmitter technology that allows a directly modulated laser (DML) to be used in high-performance applications with a smaller size, lower power consumption, less device complexity, and lower cost. The CML comprises a DML and an isolated, passive optical filter. A key feature of the CML is its large tolerance to fiber dispersion, reaching over 360 km transmission at 10 Gb/s in standard single-mode fiber without dispersion compensation. The combination of adiabatic chirp from the laser and filter edge response produces high extinction ratio pulses with nearly uniform phase, abrupt phase shifts at bit transitions, and a correlation between the 1 bits; 1 bits separated by odd number of 0 bits are out of phase. This results in destructive intersymbol interference after fiber transmission. Other applications of CML are generation of advanced modulation formats, such as return-to-zero (RZ) alternate mark inversion, and RZ differential phase-shift keying. Tunable CML using DFB array, and sampled grating deterministic bit rate (DBR) technologies for 10 Gb/s metro applications have now been demonstrated. A four-element DBR array CML has also been demonstrated for 100 Gb/s metro applications. This paper reviews the principle of operation of CML and its various applications, as well as recent advances in CML-based devices.

Applications of 40-Gb/s Chirp-Managed Laser in Access and Metro Networks

We investigate 40-Gb/s cost-efficient transmitter for access and metro networks. This 40-Gb/s transmitter comprises a standard directly modulated distributed-feedback (DFB) laser and a subsequent optical filter. Large dispersion tolerance of this transmitter is realized by chirp control through the phase correlation between adjacent bits for the destructive interference in order to erase the power of ldquo0rdquo bits while enhancing the extinction ratio. The chirp model of the DFB laser and the optimum parameters of the optical filter have been numerically analyzed. The chirp-managed 42.8-Gb/s transmission over 20-km standard single mode fiber (SSMF or SMF-28) without dispersion compensation and a centralized lightwave WDM-PON system are experimentally demonstrated. We have also realized the transmission over 100-m graded index plastic optical fiber (GI-POF). Moreover, the application in the metro network over 240-km SSMF or SMF-28 has also been investigated in this paper.

Tunable Chirp Managed Laser

We demonstrate a compact tunable chirp managed laser (CML) comprising a radio-frequency switch, a directly modulated distributed feedback laser array, a microelectromechanical systems mirror, and an optical filter and obtain error-free transmission performance over 30 nm at 10.7 Gb/s up to 200 km without electrical dispersion compensation (EDC) or optical dispersion compensation. Transmission distance is stretched to 300 km over the same wavelength range by adding a standard EDC to the receiver.

42.8 Gbit/s chirp-managed signal transmission over 20 km standard SMF at 1550 nm without DCF

Error-free transmission at 42.8 Gbit/s over 20 km of standard singlemode fibre at 1550 nm without dispersion compensation using a directly modulated chirp-managed laser is demonstrated.

Chirp-managed laser and MLSE-RX enables transmission over 1200 km at 1550 nm in a DWDM environment in NZDSF at 10 gb/s without any optical dispersion compensation

The small form factor chirp-managed laser (CML) source at 1550 nm was used in conjunction with postdetection electronic signal processing to successfully achieve transmission over 1200 km of nonzero dispersion-shifted fiber in a dense wavelength-division-multiplexing environment, without using any optical dispersion compensation. In a comparative study, the dispersion tolerance and the transmission performance of the CML were found to be better than the duobinary format.