Experimental demonstration of self-aligned InP/InGaAsP polarization converter for polarization multiplexed photonic integrated circuits

Abstract

Highly efficient, low-loss, and compact InP/InGaAsP polarization converter based on a half-ridge waveguide structure is fabricated and demonstrated experimentally. The device is fabricated by a simple self-aligned process and integrated with a ridge InP waveguide. Using a 150-μm-long device, we obtain the mode conversion of more than 96% and the on-chip loss of less than 1.0 dB over the broad wavelength range from 1510 to 1575 nm. The experimental results are explained quantitatively using the full-vector eigenmode calculation, which also reveals large fabrication tolerance of the demonstrated device.

Numerical Study on Fabrication Tolerance of Half-Ridge InP Polarization Converters

“…After forming a ridge waveguide along [011] direction by dry etching (a), we selectively wet-etch InGaAsP layer until the InP etch-stop layer, so that a precisely defined slope corresponding to the (111) plane is formed. Similar to the halfridge fabrication procedure [22], SiO 2 is deposited from an angle, covering only one side of the ridge waveguide (c). Finally, the Type 2 structure is obtained after the second dryetching (d).…”

“…2. In our previous demonstration [22], the fabricated device had a residual slope at the ridge side of the InGaAsP core as shown in Fig. 1(b), which was due to a slight anisotropic etching during the Cl 2 /Ar dry-etching process.…”

“…• slope corresponding to (111) crystal plane of the InGaAsP, which reflects the actual fabricated device [22]. The eigenmodes in each structure are calculated for various values of the width of the PC w and the residual InGaAsP thickness d at the ridge side.…”

“…In this respect, a simple PC with a ridge-like waveguide structure having large fabrication tolerances is highly desired. We have recently proposed and experimentally demonstrated a half-ridge InP/InGaAsP PC, which particularly suits the integration with LDs because of its ridge-like structure and a simple self-aligned fabrication process [21], [22]. More than 96% polarization conversion has been experimentally obtained with the PC length of 150 µm and the wide wavelength range covering the entire C-band.…”

Design and experimental investigation of monolithic polarization controller with InGaAlAs/InAlAs multiple quantum wells

“…Similarly, we have recently proposed and demonstrated a monolithic InP polarization modulator, consisting of the half-ridge polarization converter (PC) and polarization-dependent phase shifter (PD-PS) sections [9]. The half-ridge scheme offers a unique advantage that it can be fabricated by relatively simple self-aligned process and exhibits great compatibility with other ridge waveguide components [10,11]. Proof-of-concept device was fabricated and demonstrated experimentally using the Pockels effect inside the bulk InGaAsP core layer [9].…”