Lithium niobate (LN), spurred by its success for fiber-optic communications, has remained the material of choice for high-performance electrooptic (EO) modulators. The past decade has seen a surge in efforts aimed at miniaturizing LN EO modulators with higher order modulation formats, data centers, and optical interconnect applications in mind. The state-of-the-art of these compact modulators, with a focus on fabrication, design, and high-speed performance is reviewed. Guidelines for design optimization and key performance metrics of these important integrated photonic devices are presented. Furthermore, an outlook on the road toward commercial viability, along with potential novel applications is provided.

Compact Lithium Niobate Electrooptic Modulators

Optical on-off modulators require low insertion loss, high contrast ratio (CR), small drive power and large bandwidth or bit-rate. A systematic approach to optimize the total performance of these modulators based on the quantum-confined Stark effect is presented here. The approach consists of minimizing the power/bandwidth ratio while satisfying a given CR and insertion loss. Our design consists of a large-core multimode passive waveguide with a thin buried active layer. The passive waveguide is designed to yield a high coupling efficiency to conventional single-mode fibers. The quantum well material structure is designed to maximize Delta alpha / Delta F/sup 2/, while maintaining a sufficiently large Delta alpha / alpha /sub 0/, where Delta alpha is the absorption change, alpha /sub 0/ is the residual absorption at zero bias, and Delta F is the swing of the applied electric field. Our theoretical model shows that i) wider quantum wells give larger Delta alpha / Delta F/sup 2/, and ii) the bandwidth/power ratio as high as 4 GHz/mW can be achieved simultaneously with small insertion loss, For example, with a drive voltage of 3 V, an RC limited bandwidth as high as 60 GHz is predicted, while a contrast ratio of 20 dB and a total insertion loss of 4.5 dB may also be obtained. >

Theoretical design optimization of multiple-quantum-well electroabsorption waveguide modulators

The spurious-free dynamic range (SFDR) of an InGaAsP-InP Franz-Keldysh effect (FKE) waveguide modulator is studied. Low-biasing the FKE modulator is shown to enhance the SFDR by 22 dB with a 3-dB optical power penalty. Polarization-independent RF operation is also obtained with low bias. At 2 mA photocurrent, the simulated narrowband and broadband SFDR are, respectively, 127 dB and 104 dB in a 1-Hz bandwidth. The measured result projects a narrowband SFDR of 129 dB-Hz/sup 4/5/ at this photocurrent. >

Enhanced linear dynamic range property of Franz-Keldysh effect waveguide modulator

The first monolithic integration of an interferometric modulator with a gain-coupled distributed-feedback laser is reported. The integrated MZ/DFB is fabricated by butt-coupling in order to minimise design constraints on the MZ and DFB active regions. 10 Gbit/s transmission over 100 km of NDSF at λ = 1.55 µm is achieved with a receiver penalty of <1 dB. ~90% of the integrated lasers emit in a single longitudinal mode.

Mach–Zehnder modulator integrated with a gain-coupled DFB laser for 10 Gbit/s, 100 km NDSF transmission at 1.55 [micro sign]m

High-speed, low-driving-voltage operation of multiple-quantum-well (MQW) external modulators based on the quantum-confinement Stark effect (QCSE) operating at long wavelengths are reviewed We discuss the design and characteristics of ultrafast intensity and phase MQW modulators that have been developed by our group and we compare them with those of other material systems and structures based on a defined figure of merit for external modulators In addition, we discuss a new integrated light source that enables external modulation of an in-plane DFB laser to reduce wavelength chirping and coupling loss with a laser and a modulator Finally, we describe new applications for optical soliton pulse generation using the above intensity modulator © 1994 John Wiley & Sons, Inc

Multiple-quantum-well optical modulators and their monolithic integration with DFB lasers for optical-fiber communications (invited paper)

Bulk InGaAsP-InP electroabsorption optical modulators with high extinction ratio, low drive voltage, and high modulation bandwidth at lambda =1.3 mu m are reported. The devices have a tapered-fiber-to-modulator-to-tapered-fiber extinction ratio greater than 20 dB at a drive voltage of >

High-speed bulk InGaAsP-InP electroabsorption modulators with bandwidth in excess of 20 GHz

Single-mode and high-power operation at temperatures up to 120/spl deg/C has been achieved in 1.3-/spl mu/m strained MQW gain-coupled DFB lasers. A stable lasing wavelength is maintained due to a large modal facet loss difference of the two Bragg modes, which is provided by the gain-coupling effect. A very low temperature dependence of the threshold current has been obtained by detuning the lasing wavelength to the long wavelength side of the material gain peak at room temperature, which effectively compensates the waveguide loss at higher temperatures. An infinite characteristic temperature T/sub o/ can be realized at certain ranges of temperature depending on the detuning value. >

C. Blaauw

Papers

High-speed bulk InGaAsP-InP electroabsorption modulators with bandwidth in excess of 20 GHz

High-temperature single-mode operation of 1.3-μm strained MQW gain-coupled DFB lasers