Digital Supermode Distributed Bragg Reflector Research Articles

Fiber Bragg Grating Interrogation System Based on the Laser Wavelength Modulation in a Digital Supermode -Distributed Bragg Reflector Laser

In this paper, we propose a Fiber Bragg Grating (FBG) interrogation system based on the modulation of the laser wavelength. Key component of the interrogation scheme is in a Digital Supermode -Distributed Bragg Reflector (DS-DBR) Laser. The DS-DBR features a large spectral range and a fast modulation capability in a low cost device. When the laser spans over the FBG spectral range, the power of the reflected signal changes over time according the FBG spectral shape. The information on the Bragg wavelength can be extracted from the modulated signal reflected by the FBG in the time domain. We implemented the proposed interrogation scheme by discrete components demonstrating its capability to retrieve the Bragg wavelength of one or more FBGs. The interrogation system features an intrinsic tradeoff between spectral resolution and interrogation speed. A Bragg wavelength resolution of 1.5 pm has been obtained using 1 kHz modulating frequency. The proposed interrogation system is particular suited in applications in which an adaptive interrogation strategy can be conveniently adopted.

Suppression of thermal wavelength drift in widely tunable DS-DBR laser for fast channel-to-channel switching.

We present a simple and effective method for suppressing thermally induced wavelength drift in a widely tunable digital supermode distributed Bragg reflector (DS-DBR) laser monolithically integrated with a semiconductor optical amplifier (SOA). For fast thermal compensation, pre-compensatory currents are injected into the gain medium section of the DS-DBR laser and the SOA. This method can be easily applied to existing commercial tunable lasers, since it is implemented without any modification to manufacturing process. Experimental results exhibit that wavelength stability is noticeably improved to ± 0.01 nm. We also experimentally demonstrate a fast channel-to-channel switching in a wavelength-routed optical switching system employing a 90 × 90 arrayed waveguide grating router (AWGR). The measured switching time is less than 0.81 µs.

Fast Wavelength Switching Transceiver for a Virtualized Coherent Optical Network

Fast reconfigurable digital coherent transceivers will become a key subsystem in future virtualized optical networks as they provide the ability to tailor the channel frequency, symbol rate, and modulation format. This transceiver agility is of paramount importance for network resilience, bandwidth on demand applications, and congestion aware routing. We demonstrate a fast wavelength switching coherent transceiver based on semiconductor tunable lasers and a parallelized digital signal processing implementation. The inherent frequency and phase noise associated with semiconductor tunable lasers is analyzed and a dc pilot tone assisted phase noise mitigation technique is proposed for a fast wavelength switching dual-polarization orthogonal frequency-division multiplexed transceiver. This enables the use of commercially available digital supermode distributed Bragg reflector lasers in both the transmitter and receiver in an 800-km wavelength routed coherent network that exhibits a variable path history.

First Demonstration of a WDM-PON System Using Full C-band Tunable SFP+ Transceiver Modules [Invited

In this paper, a wavelength-division-multiplexing passive optical network (WDM-PON) system using small form-factor pluggable plus (SFP+) packaged full C-band tunable transceivers is demonstrated for the first time to our knowledge. Within the transceivers, a novel digital-supermode distributed Bragg reflector (DS-DBR) laser with a monolithically integrated Mach–Zehnder modulator is employed as the transmitter. A generic current control algorithm is used to drive the DS-DBR laser, which employs a laser current training sequence ensuring successful operation without the need for individual laser characterization. A pilot-tone-based feedback control loop is implemented using embedded hardware, which is able to lock the output wavelengths from three identical optical network units with less than ±3  GHz deviation from their assigned channels. Error-free transmission is achieved at a 10 GbE data rate. With the feedback control loop running continuously, the system shows a sensitivity of −23  dBm for a bit error rate of 10−12.

Fast Wavelength Switching 6 GBd Dual Polarization 16QAM Digital Coherent Burst Mode Receiver

A commercially available digital supermode distributed Bragg reflector tunable laser is employed as a fast wavelength switching local oscillator (LO) in a dual polarization (DP) 16-quadrature amplitude modulation (16QAM) coherent burst mode receiver. A digital coherence enhancement technique is used to compensate both the Lorentzian and non-Lorentzian distributed phase noise of the tunable LO laser. It is shown that differential decoding is not sufficient to overcome the substantial bit errors caused by the LO laser phase noise. However, the coherence enhancement technique enables the reception of low symbol rate DP-16QAM bursts, with an average optical signal to noise ratio penalty of 3.5 dB observed relative to theory at the forward error correction threshold (1.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ).

Using a DS-DBR laser for widely tunable near-infrared cavity ring-down spectroscopy

Studies into the suitability of a novel, widely tunable telecom L-band (1,563–1,613 nm) digital supermode distributed Bragg reflector (DS-DBR) laser for cavity ring-down spectroscopy (CRDS) are presented. The spectrometer comprised of a 36.6 cm long linear cavity with ring-down times varying between 19–26 μs across the 50 nm DS-DBR wavelength range due to changes in the cavity mirror reflectivities with wavelength. The potential of such a broadband, high-resolution CRD spectrometer was illustrated by investigating several transitions of CO2 in air, a 5 % calibrated mixture and breath samples. Allan variance measurements at a single wavelength indicated an optimal minimum detectable absorption coefficient (α min) of 3 × 10−10 cm−1 over 20 s.

Digital Coherent Receivers for Long-Reach Optical Access Networks

The relative merits of coherent-enabled optical access network architectures are explored, with a focus on achievable capacity, reach and split ratio. We review the progress in implementing the particular case of the ultra dense wavelength division multiplexed (UDWDM) passive optical network (PON), and discuss some challenges and solutions encountered. The applicability of digital signal processing (DSP) to coherent receivers in PONs is shown through the design and implementation of parallelized, low-complexity application-specific digital filters. In this work, we focus on mitigating the impact of local oscillator laser (LO) relative intensity noise (RIN) on receiver sensitivity, and propose an algorithm which compensates for this impairment. This phenomenon is investigated theoretically and then experimentally by evaluating the sensitivity of a coherent receiver incorporating different tunable light sources; a low-RIN external cavity laser (ECL) and a monolithically integrated digital supermode distributed Bragg reflector (DS-DBR) laser. It is shown that the RIN of the signal laser does not significantly contribute to the degradation of the receiver sensitivity. Finally, a 10 Gbit/s coherent PON is demonstrated using a DS-DBR laser as the LO laser. It is found that a receiver sensitivity of -38.8 dBm is achievable assuming the use of hard-decision forward error correction.

Combining a DS-DBR laser with QPM-DFG for mid-infrared spectroscopy

Studies into the suitability of a novel, widely tunable telecom L-band (1563–1613 nm) digital supermode distributed Bragg reflector (DS-DBR) laser for spectroscopy in the mid-IR are presented. Light from the DS-DBR laser was mixed with 1064 nm radiation in a periodically poled lithium niobate (PPLN) crystal to generate mid-IR light by quasi phase matching difference frequency generation (QPM-DFG). The resultant continuous wave radiation covered the range 3000–3200 cm−1 with powers of up to 2.6 μW. The use of such laser light for spectroscopic applications was illustrated by performing absorption experiments on both narrow-band and broad-band absorbers, namely methane (CH4) and methanethiol (CH3SH). Wavelength modulation spectroscopy (WMS) on CH4 demonstrated that the modulation characteristics of the DS-DBR laser observed in the near-IR were transposed to the mid-IR and yielded a sensitivity of 3.1×10−6 cm−1 Hz−1/2 over a 47 cm path length. In the CH3SH spectrum, the absorption feature at 3040 cm−1 was identified as a potential useful region for monitoring this biomarker in exhaled breath at reduced pressures.

Demonstration of a widely tunable digital supermode distributed Bragg reflector laser as a versatile source for near-infrared spectroscopy

In this paper we report the characterization of a novel, widely tunable, diode laser source operating over the full telecom L-band (1563–1613 nm), namely the digital supermode distributed Bragg reflector (DS-DBR) laser, and its application to multi-wavelength gas sensing via absorption strategies. The spectroscopic performance of the laser has been assessed by investigating the ro-vibrational spectrum of CO2, and wavelength modulation spectroscopy was accomplished for proof-of-principle sensitive measurements in discrete spectral regions.

Equivalent Performance in C- and L-Bands of Digital Supermode Distributed Bragg Reflector Lasers

New results on the design and performance of digital supermode distributed Bragg reflector lasers for L-band operation are presented. The L-band device, which is fabricated using the same InP-based process as its C-band equivalent is shown to give essentially the same performance. The design changes required are discussed and a detailed comparison presented between C- and L-band devices. Together, a two-chip solution can provide more than 200 consecutive 50-GHz spaced channels (82-nm bandwidth) with SMSR greater than 45 dB and fiber-coupled leveled powers of 13 dBm.

Monolithic digital supermode distributed Bragg reflector laser with record tuned ex-facet power in excess of 20 dBm over C-band

An improved digital supermode distributed Bragg reflector laser with a monolithically integrated semiconductor optical amplifier with ex-facet output powers greater than 20 dBm over the full C-band is reported. In addition, the sidemode suppression ratio was greater than 40 dB over the full tuning range.

Modelling of phase-grating based wideband tuneable lasers with simplified quasi-digital wavelength selection

A transfer matrix based model is discussed which was used to simulate a novel wideband tuneable laser design. This model can simulate the predicted behaviour of an arbitrary, multi-section distributed Bragg reflector (DBR) laser and can successfully predict tuning behaviour, threshold current, output power and static side-mode suppression ratio. The particular DBR laser, the digital super-mode DBR (DS-DBR), tunes by means of a highly uniform comb of narrow reflection peaks coupled with a multi-grating structure that can be used to digitally select a sub-band of the total tuning range. By selecting sub-bands in turn, the whole tuning range of the device can be accessed. Results of the model are compared with experimental results for this device which show a tuning range of around 50 nm, together with output powers in the range 8-9 dBm and a side-mode suppression ratio of better than 50 dB over 80 WDM channels at 50 GHz spacing. These results are for a device packaged in a standard 26-pin butterfly module.