Characterization of wavelength tunable lasers for future optical communication systems

The use of tunable lasers (TL) in dense wavelength division multiplexed (DWDM) networks for optical switching, routing and networking has gained a lot of interest in recent years. Employment of such TLs as tunable transmitters in wavelength packet switched (WPS) networks is one of the possible applications of these devices. In such systems, the information to be transmitted could be encoded onto a destination dependent wavelength and the routing of traffic could be performed on a packet-by-packet basis. The authors investigate the possibility of using TLs in DWDM WPS networks by focusing on the characterisation of the instantaneous frequency drift of a TL due to wavelength tuning and direct modulation. Characterization of the linewidth of the TLs is also presented to verify the feasibility of using TLs in systems employing advanced modulation formats

Perancangan Sistem Pengukuran Tunability Laser DFB Dengan Teknik Heterodyne Beat Signal

Abstrak Pengukuran tunability laser merupakan salah satu cara untuk mengetahui kemampuan tala dari sebuah laser. Tunability laser menyatakan kemampuan tala panjang gelombang laser yang dipengaruhi oleh variabel kontrol. Selama ini pengukuran tunability laser dilakukan menggunakan Optical Spectrum Analyzer (OSA) yang memiliki performansi pengukuran tidak cukup baik utamanya bila laser akan digunakan untuk keperluan khusus seperti pembangkit mm-wave. Pada penelitian ini telah dilakukan perancangan sistem pengukuran tunability laser dengan teknik heterodyne beat signal yang terdiri atas laser Distributed Feedback Laser (DFB) tipe Anritsu dan Eudyna, fiber coupler, OSA, fotodetektor dan RF Spectrum Analyzer. Laser DFB memiliki kemampuan tala dan kestabilan frekuensi terbangkit yang baik. Pengukuran tunability laser dengan teknik heterodyne beat signal memiliki kelebihan dapat meningkatkan keakurasian dan kepresisian pengukuran dengan memanfaatkan dua buah laser yang menghasilkan sinyal berfrekuensi tinggi. Pengambilan data dalam pengujian ini melalui pemaduan dua sinyal laser yang bertujuan untuk memperoleh frekuensi pelayangan yang mampu tala oleh variasi arus injeksi dan temperatur operasional. Sinyal hasil pelayangan dideteksi menggunakan RF Spectrum Analyzer. Selanjutnya daya sinyal diamplifikasi dengan amplifier eksternal dan diuji kepresisiannya sebelum diaplikasikan dalam Sistem Komunikasi Serat Optik secara auto-tune. Hasil yang diperoleh adalah tunability laser sebesar 0,578-8,395 GHz pada rentang temperatur 32,87◦C sampai 34,90◦C dengan step pengukuran perbedaan temperatur sebesar 0,07◦C dengan kepresisian mencapai 97,8554%. Hasil pengukuran menunjukkan bahwa perubahan frekuensi laser terhadap temperatur sebesar 9,06 GHz/◦C dan bila pengukuran langsung menggunakan OSA perubahannya sebesar 11,44 GHz/◦C. Daya terbesar beat signal hasil amplifikasi menggunakan amplifier 4-8 GHz dengan x gain 25 dB adalah -38,9179 dBm, lebih kecil dari daya yang dibutuhkan untuk membangkitkan prescaller sebesar -15 dBm. Sinyal hasil amplifikasi mempunyai SNR sebesar 32 dB sehingga masih memungkinkan untuk diamplifikasi lagi. ================================================================================================= Measurement of laser tunability is one way to determine the ability of a laser tuning. Laser tunability stating wavelength of laser that tuning capabilities are influenced by control variables. During this measurement of laser tunability by using Optical Spectrum Analyzer (OSA) which has the measurement performance is not good specially for mm-wave generation. This study has been carried out design of laser tunability measurement system by using heterodyne beat signal technique consist of Distributed Feedback Laser (DFB) laser Anritsu and Eudyna, fiber coupler, OSA, photodetector, and RF Spectrum Analyzer. DFB laser has the ability of tuning and good frequency stability. Measurements of laser tunability with heterodyne beat signal techniques can increase the accuracy and precision of measurement with utilizes two lasers that generate high-frequency signals. Collecting data in this experiment through the integration of two laser signals aimed to obtain beat- frequency capable of tuning by variation of injection current and operating temperature. The signal was detected using RF Spectrum Analyzer. Furthermore amplified signal power with external amplifier and precision test before applied in the Optical Fiber Communication System in auto-tune. The results obtained laser tunability are 0.578 to 8.395 GHz from 32,87◦C till 34,90◦C with step difference temperature of measurement each 0,07◦C with precision reached 97.8554%. The measurements’result show that alteration frequency of laser toward temperature are 9,06 GHz/◦C and 11,44 GHz/◦C if by using direct measurement with OSA.The biggest beat signal’power amplification product is -38.9179 dBm using the 4-8 GHz amplifier with gain is 25 dB which is smaller than power is needed to xii prescaller generation as big as -15 dBm. The amplified signal has SNR 32 dB and this signal can be amplify again

Characterisation of optimum devices and parameters for enhanced optical frequency comb generation

The Internet has become an irreplaceable aspect of our daily life. It is used every day by billions of people around the world for various functions such as business, study, and entertainment. Hence, an unabated rise in the demand for higher and faster data traffic has been experienced through the last few decades. This demand for bandwidth is further fuelled by the introduction of bandwidth intensive applications such as ultra-high-definition video streaming, real time online gaming and cloud services making the realization of higher capacity and performance optical networks a necessity. Today’s telecommunication systems are static, with pre-provisioned links requiring an expensive and time-consuming reconfiguration process. The state-of-the-art approach (wavelength division multiplexing - WDM), entailing multiple lasers emitting differing wavelengths (each modulated) multiplexed together (on a 50 GHz grid), cannot meet the growing demands. Hence, future networks need to be flexible and programmable, allowing for resources to be directed, where the demand exists, thus improving network efficiency. A cost-effective solution is to utilise the legacy fibre infrastructure more efficiently by reducing the size of the guard bands and allowing closer optical carrier spacing, thereby increasing the overall spectral efficiency. However, such a scheme imposes a stringent transmitter requirement in terms of wavelength stability, noise properties and cost-efficiency, which would not be met with the incumbent laser-array based transmitters. An attractive alternative would be to employ an optical frequency comb (OFC), which generates multiple phase-correlated optical carriers with a precise frequency separation. The reconfigurability of such a multi-carrier transmitter would enable tuning of channel spacing, number of carriers and emission wavelengths, according to the dynamic network demands. This thesis focusses on the externally injected gain-switched laser-based OFC (GSL-OFC) technique. Advances to the state of the art are achieved via a detailed static and dynamic characterisation of lasers, which is then used for enhancing the comb generation process. Specifically, initial efforts are devoted to the use of different laser structures for OFC generation. This aspect is then furthered by incorporating the concept of photonic integration to reduce the cost, power consumption and footprint of the multi-carrier transmitter. Self and externally seeded photonic integrated circuits are used to generate combs that are then fully characterized to verify their employability in optical networks