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DISABLING PER-CHANNEL LIGHT SOURCES WITH SILICON PHOTONIC-BASED VARIABLE OPTICAL ATTENUATOR

IP.com Disclosure Number: IPCOM000248985D
Publication Date: 2017-Jan-25
Document File: 3 page(s) / 402K

Publishing Venue

The IP.com Prior Art Database

Related People

Norman Tang: AUTHOR [+4]

Abstract

Many multi-channel optical transceiver modules share a laser diode across two channels or more. The light source from the laser diode is split by an optical beam splitter into two separate channels before entering the optical modulator. A variable optical attenuator (VOA) is added after the optical modulator for each lane. The VOA operates as an on/off switch to control the per-channel light sources via the Tx_Disable function of the module.

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Copyright 2017 Cisco Systems, Inc. 1

DISABLING PER-CHANNEL LIGHT SOURCES WITH SILICON PHOTONIC- BASED VARIABLE OPTICAL ATTENUATOR

AUTHORS: Norman Tang

Nick Peng David Lai

Anthony Nguyen

CISCO SYSTEMS, INC.

ABSTRACT

Many multi-channel optical transceiver modules share a laser diode across two

channels or more. The light source from the laser diode is split by an optical beam splitter

into two separate channels before entering the optical modulator. A variable optical

attenuator (VOA) is added after the optical modulator for each lane. The VOA operates as

an on/off switch to control the per-channel light sources via the Tx_Disable function of the

module.

DETAILED DESCRIPTION

In response to the surge in demand for high-density 10G and 25G connectivity,

multi-channel optical transceivers (e.g., Quad Small Form-factor Pluggable (QSFP)+

4x10G, QSFP28 4x25G, etc.) are becoming increasingly popular. Many of these modules

do not have an independent laser diode for each channel. Rather, one laser diode is shared

among two or more channels, and uses an optical modulator for manipulating a property

of light for each user data channel. However, the modulator can only suppress the optical

power down to -20 dBm, as opposed to -30 dBm as required by the relevant Institute of

Electrical and Electronics Engineers (IEEE) specification for TX off. This results in the

partner port not detecting light removal and failing to assert Rx_Los. Shutting the laser

diode down directly is not desirable either as doing so would also turn off the light of the

adjacent channel because of low granularity.

As described further herein, a VOA is added after the optical modulator to suppress

the laser power for each channel. The VOA may be integrated within the waveguide of the

Copyright 2017 Cisco Systems, Inc. 2

silicon photonics substrate, for a low-cost implementation. The VOA enables optical power

suppression of -30dBm without requiring a large forward bias current on the VOA.

Figure 1 below illustrates a high-level diagram of a portion of an Nx10G/25G...