Song, Ju Bin; (2002) Multichannel optical frequency generation using quantum confined Stark effect tuned lasers for dense wavelength division multiplex applications. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In future dense wavelength division multiplex (DWDM) systems, highly stable sources will be required. This thesis describes a 1.55 μm multichannel source for DWDM using InGaAsP/InP multiple quantum well (MQW) quantum confined Stark effect (QCSE) tuning and an investigation of the use of InGaAsP/InP MQW QCSE frequency modulated (FM) lasers as potentially compact and low cost optical comb generators for DWDM applications. Firstly, using quaternary InGaAsP MQW systems, large area and low parasitic capacitance fast QCSE air bridged modulators have been designed and demonstrated which could be used in a QCSE FM laser comb generator. The reverse breakdown voltage was over -20 V with a few nA leakage current. The refractive index change was measured as 1.25% at 40 kV/cm electric field. The 3 dB cut off frequency of the air-bridged QCSE modulator was greater than 6 GHz. Secondly, a multichannel source which has a frequency that can be selected from a wide range of values and which uses an InGaAsP/InP MQW QCSE tuned external cavity structure has been demonstrated. The InGaAsP/InP gain laser is coupled to a MQW QCSE modulator including a distributed Bragg reflector (DBR) mirror. The selectable channel bandwidth was 32 nm with 25 dB side mode suppression which can be reduced further by adjusting the external cavity condition, 1 dB gain flatness over the range, and 140 GHz channel spacing which can be changed to suit the 100 GHz ITU or other WDM grids by using a gain laser of an appropriate length. Thirdly, the first demonstration of comb line generation using InGaAsP MQW QCSE tuned semiconductor FM laser operation is described. For this demonstration a novel external cavity structure was used involving fast InGaAsP/InP MQW QCSE optical modulators and an anti-reflection coated gain laser. 20 significant comb lines can be achieved before multimode operation due to modulation frequency induced instability occurs. Finally, dense wavelength division multiplex systems employing a semiconductor FM laser comb generator and injection locked techniques are discussed.

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