Ultracompact monolithic integration of balanced, polarization diversity photodetectors for coherent lightwave receivers

Abstract

Abstract-We monolithically integrate an optical front-end on InP for balanced, polarization-diversity coherent lightwave reception which is only 1 3 mm long. Low on-chip insertion loss (<4.5 dB) and balanced photoresponse (1.05:l or better) are achieved at 1.5 pm wavelength using straightforward, regrowth-free fabrication. Low capacitance photodetectors ( I 0.15 pF) are employed for high bandwidth operation.ONOLITHIC integration of optical waveguide de-M vices with other optoelectronics enhances on-chip functionality, and improves packaging cost and reliability by minimizing hybrid optical interconnections. A target application for such integration has been coherent lightwave receiver front-ends, combining photodetectors with 3 dB waveguide couplers for balanced operation [11-[6] and polarization-splitting optics for polarization-insensitive reception using diversity architectures [5], [6]. Compatibility with high 111-V materials' cost, however, requires high-yield integration processes and compact device size. The large size, typically several millimeters, of waveguide couplers with associated input-output branching is a serious obstacle to cost-effective monolithic integration. We previously reported alternative approaches for ultra-compact 3 dB couplers [7] and polarization-selective detectors [8]. Here we integrate both device types on a single InP chip to realize an ultracompact (1.3 x 0.4 mm'), balanced, polarization-diversity photodetector which is easy to fabricate (no epitaxial regrowth, minimal photolithography) and exhibits low detector capacitance (< 0.15 pF).Our device (Fig. 1) consists of two single-mode input rib waveguides for photosignal and local oscillator (LO) inputs, a multi-mode interference [9] (MMI)

Silicon photonic integration in telecommunications

“…The first reported coherent receivers were in InP, as shown in Figure 24A [51][52][53][54][55]. Figure 24B shows an early dual-polarization, dual-quadrature receiver in silicon photonics [56].…”

1.55‐μm surface‐illuminated monolithically integrated balanced metal semiconductor metal photodetectors and coplanar waveguide

“…A 6-dB signal improvement and a 24-dB noise cancellation were measured [3]. In these experiments the MSM was used because it has the advantage of having a symmetric I-V relation compared to p-i-n photodetectors [5][6][7][8]. Therefore, the direction of the current can be controlled by changing the polarity of the bias.…”

Multimode Interference 3 dB Splitters in Hollow Core Metallic Waveguides for Low-Loss THz Wave Transmission

“…Multimode Interference (MMI)-based devices have been established for use in several wavelength-division multiplexing (WDM) systems, such as power splitters [10], and phasedarray de-multiplexers [11] and balanced coherent receivers [12], due to the ease of fabrication, compactness, low-loss, wide bandwidth and low polarization dependence. MMI devices are based on the self-imaging property [13], where the guided modes of a multimode waveguide are excited and interfere constructively to produce single or multiple images of an input field launched usually via single mode optical waveguides at the one end of the structure, at periodic intervals along the direction of propagation.…”