Mach-Zehnder modulators

Compared to the Mach-Zehnder modulator, the modulation efficiency of the birefringent modulator is lower because is 1.5 times higher, ie,... 

Figure 4.14 Three different electrooptic waveguide devices [1] (a) Mach-Zehnder modulator with push-pull arrangement of the electrodes, (b) electrically controlled directional coupler, (c) coupler with phase-reversal electrodes.

Figure 4.15 Illustration of the constructive and destructive interference pattern in a Mach-Zehnder waveguide modulator. Only if the outgoing waveguide is single mode, the resulting antisymmetric mode will be completely radiated into the substrate. A multimode waveguide cannot be used for an efficient Mach-Zehnder modulator...

Figure 4.16 The observed cos2 (//) signal from a Mach-Zehnder modulator. A phase mismatch of 7r gives one full modulation amplitude. The pattern is completely periodic for higher values of the phase mismatch...

For waveguide phase modulators and especially the Mach-Zehnder modulator, there are two main electrode configurations, which are explained in Figure 4.18. 

IPITEK (formerly TACAN) Corporation (Carlsbad, CA) has achieved 0.8 V VK values using 3-cm interaction length push-pull Mach-Zehnder modulators, as illustrated in Fig. 33 [6,252, 302]. With 2-cm interaction length modulators, an average VK value of 1.1 V was obtained [6,252,302]. 

Researchers at Lockheed-Martin have fabricated push-pull Mach-Zehnder modulators using FTC in APC. They observed drive voltages near 1 V and these modulators exhibited good stability for periods of 3 months (with stability testing continuing) [253]. 

Fig.17a,b. TMoo single-mode pattern in channel waveguide (a) and intensity modulation response of Mach-Zehnder modulator (b)... 

FIGURE 6.16 A photograph of a Mach-Zehnder modulator manufactured by Lumera is shown. 

Paloczi, G.T., Y. Huang, A. Yariv, J. Luo, and A. Jen. 2004. Replica-molded electro-optic polymer Mach-Zehnder modulator. Appl Phys Lett 85 1662-1664. 

J. W. Kang, J. J. Kim, E. Kim, All-optical Mach-Zehnder modulator using a photochromic dye-doped polymer,... 

Arrioja D. A. May, P. LiKamWa, I. Shubin, P.KL. Yu (2008) "Integrated InGaAsP MQW Mach-Zehnder modulator" Microelectronics Journal, Volume 39, Issues 3-4, March-April... 

For a low-frequency, Mach-Zehnder modulator, the impedance is dominated by the electrode capacitance and resistance as shown in Fig. 9.57. A Smith chart plot for a MZM is shown in Fig. 9.58. Unlike the laser diode, a modulator on lithium niobate has no junctions consequently the impedance is independent of modulator bias. As was the case with the diode laser, it is often important to match the modulator impedance to the system impedance, typically 50 or 75 real. However, unlike the diode laser, modulators fabricated in electro-optic materials that are also piezoelectric can have perturbations in their impedance due to coupling of some of the modulation signal into compressional waves. The coupling can be significant at frequencies where the modulator crystal is resonant. The dashed curve in Fig. 9.58 shows an acoustic resonance at 150 MHz. A number of techniques (Betts, Ray and Johnson, 1990) have been developed to suppress these acoustic modes to insignificant levels, as is evidenced by the solid curve in Fig. 9.56. 

FIGURE 9.60 Mach-Zehnder modulator IM-free DR with modulator biased at V jl. 

Farwell, M.L., Chang, W.S.C., and Huber, D.R. 1993. Increased linear dynamic range by low biasing the Mach-Zehnder modulator. IEEE Phot Tech. Lett. 3 779-782. 

In 1991, the first Pl-based guest-host electro-optical (EO) systems were described [216,217] and the example of fabrication of an all-PI Mach-Zehnder modulator of a vertical triple-stack with the cladding PI-EO-core Pl-cladding PI sandwiched between electrodes using a commercial laser dye DCM [4-(dicyano-methylene)-2-methyl-6-(p-dimethylaminostyryl)-4H pyran] is given in a monograph [215] in order to show the development pathway of a prototype device in the use of polyimides for EO devices. 

---