Compact InP Stokes-Vector Modulator and Receiver Circuits for Short-Reach Direct-Detection Optical Links

Abstract

To meet the demand for continuous increase in data traffic, full usage of polarization freedom of light is becoming inevitable in the next-generation optical communication and datacenter networks. In particular, Stokes-vector modulation direct-detection (SVM-DD) formats are expected as potentially cost-effective method to transmit multi-level signals without using costly coherent transceivers in the short-reach links. For the SVM-DD formats to be practical, both the transmitter and receiver need to be substantially simpler, smaller, and lower-cost as compared to coherent counterparts. To this end, we have recently proposed and demonstrated novel SV modulator and receiver circuits realized on monolithic InP platforms. With compact non-interferometric configurations, relatively simple fabrication procedures, and compatibility with other active photonic components, the proposed devices should be attractive candidate in realizing low-cost monolithic transceivers for SVM formats. In this paper, we review our approaches as well as recent progresses and provide future prospects.

Design of InGaAsP phase modulator with asymmetrically coupled quantum wells for efficient polarization modulation

“…Figure 1 shows the schematic and cross-sections of InP-based straight-line polarization modulator, 20,23) which consists of a pair of PC and PD-PM sections concatenated in series. The passive PC section with asymmetric waveguide cross-section is employed to provide a fixed rotation of the Stokes vector (SV) on the Poincaré sphere.…”

“…[10][11][12][13][14][15][16] While polarization modulators based on discrete components were commonly used in the previous system experiments, integrated polarization modulators are desired to achieve significant reduction in cost, size, and power consumption. [17][18][19][20][21][22][23][24] Among a variety of approaches, InP-based straight-line polarization modulators are attractive due to its simplicity, compactness, and capability of monolithically integrating active components, such as lasers and semiconductor optical amplifiers. [20][21][22][23][24] By cascading multiple stages of polarization converters (PC) and polarization-dependent phase modulators (PD-PM), we can convert the input light in the transverse-electric (TE) or transverse-magnetic (TM) mode to an arbitrary state-of-polarization (SOP) at the output.…”

“…[17][18][19][20][21][22][23][24] Among a variety of approaches, InP-based straight-line polarization modulators are attractive due to its simplicity, compactness, and capability of monolithically integrating active components, such as lasers and semiconductor optical amplifiers. [20][21][22][23][24] By cascading multiple stages of polarization converters (PC) and polarization-dependent phase modulators (PD-PM), we can convert the input light in the transverse-electric (TE) or transverse-magnetic (TM) mode to an arbitrary state-of-polarization (SOP) at the output. For efficient modulation, a PD-PM with a large polarization dependence is required.…”

Polarization coupler for polarization-rotating Mach-Zehnder interferometer

“…In PICs, the polarization rotator is important for polarization diversity and polarization control systems [1][2][3][4][5][6]. Conventionally, to realize mode conversion between the transverse electric (TE) and transverse magnetic (TM) modes, the optical axis is rotated by 45° similar to a half-wave plate by employing a waveguide structure with asymmetry in the horizontal and vertical directions [7][8][9][10][11][12][13].…”

“…When a Mach−Zehnder interferometer (MZI) is composed of the proposed 3 dB coupler, the polarization of the output light is rotated depending on the phase difference between the two arms. This MZI can operate as a tunable polarization rotator, and is simpler than conventional polarization rotators [3][4][5][6]21]. By incorporating optical phase shifters, such as MZ switches or modulators, polarization rotation can be controlled.…”