Compact and Athermal DQPSK Demodulator with Silica-Based Planar Lightwave Circuit

Yusuke NASU  Yohei SAKAMAKI  Kuninori HATTORI  Shin KAMEI  Toshikazu HASHIMOTO  Takashi SAIDA  Hiroshi TAKAHASHI  Yasuyuki INOUE  

IEICE TRANSACTIONS on Electronics   Vol.E93-C    No.7    pp.1191-1198
Publication Date: 2010/07/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E93.C.1191
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Optoelectronics
differential quadrature phase-shift keying (DQPSK),  Mach-Zehnder,  Delay-line interferometer,  optical planar waveguides,  

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We present a full description of a polarization-independent athermal differential quadrature phase shift keying (DQPSK) demodulator that employs silica-based planar lightwave circuit (PLC) technology. Silica-based PLC DQPSK demodulator has good characteristics including low polarization dependence, mass producibility, etc. However delay line interferometer (DLI) of demodulator had the large temperature dependence of its optical characteristics, so it required large power consumption to stabilize the chip temperature by the thermo-electric cooler (TEC). We previously made a quick report about an athermal DLI to reduce a power consumption by removing the TEC. In this paper, we focus on the details of the design and the fabrication method we used to achieve the athermal characteristics, and we describe the thermal stability of the signal demodulation and the reliability of our demodulator. We described two athermalization methods; the athermalization of the transmission spectrum and the athermalization of the polarization property. These methods were successfully demonstrated with keeping a high extinction ratio and a small footprint by introducing a novel interwoven DLI configuration. This configuration can also limit the degradation of the polarization dependent phase shift (PDf) to less than 1/10 that with the conventional configuration when the phase shifters on the waveguide are driven. We used our demodulator and examined its demodulation performance for a 43 Gbit/s DQPSK signal. We also verified its long-term reliability and thermal stability against the rapid temperature change. As a result, we confirmed that our athermal demodulator performed sufficiently well for use in DQPSK systems.