Useful Info about Optical interconnections

Optical interconnections are utilized to meet the increased level of demand pertaining to internet data traffic and to overcome the limitations of electrical interconnects due to advantages such as a short signal delay, a light weight, lower power consumption, and immunity to electromagnetic interference.

Optical interconnects improve the speed and quality of data transmissions in short-reach applications such as data processing units, optical storage applications and in data centers.

The high-storage data processing units of data centers require high-speed data transmission for rack-to-rack, board-to-board and chip-to-chip interconnections, with a design of high-capacity and compact pluggable optical modules for bidirectional optical links. Thus, careful designs of the TRx modules and optical components are desirable to minimize the optical assembly costs while optimizing their performances.

Bidirectional optical links as up- and down-links can be operated in full-duplex or half-duplex mode. During full-duplex mode operation, the optical signals can be transmitted and received simultaneously, while in half-duplex mode, the optical signals can be transmitted or received by time-sharing.

Half-duplex bidirectional transmission can be implemented through a single fiber or through two fibers. Full-duplex bidirectional transmission has been implemented through two fibers.

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In half-duplex optical interconnect applications, the bandwidth of the bidirectional data transmission is reduced, while in full-duplex data transmission, the efficiency is increased by simultaneous data transmission.

However, implementation of the full-duplex mode with two fibers increases the number of fibers for bidirectional transmission. An ideal solution to provide rapid data access in a cost-effective structure is full-duplex transmission through a single fiber.

However, simultaneous data transmission through a single fiber may cause serious interference between the up- and down-link. Hence, in the proposed bidirectional optical link, we use different wavelengths for the up- and down-link to reduce the optical crosstalk between the up- and down-link through a single fiber.

The design of a bidirectional optical link using a single fiber requires special structures and the integration of a laser diode (LD), a photodiode (PD), and a transceiver (TRx) chip with a surface mirror or a bulk optic mirror. In an early work on a bidirectional module structure using a single fiber, a silicon optical bench (SiOB) with silicon surface mirrors was shown to be capable of surface emitting/receiving LD/PD chips which are monolithically integrated with a TRx chip and mounted on the SiOB.

In other work on a bidirectional optical subassembly (OSA) module through a single-mode fiber (SMF), two long wavelengths for the up- and down-link were utilized using a bulk optical mirror in which a wavelength filter was inserted. However, these bidirectional structures use specialized TRx chips integrated with LD and PD components and complex light-transmission structures with bulky mirrors.

Therefore, we propose a simplified bidirectional OSA module with the mirror and wavelength filters fabricated into the fiber. In order to reduce the optical crosstalk, two wavelengths of 850 nm and 1060 nm are utilized for the up- and down-link, respectively, which provides wider wavelength separation and thus reduces the interference noise between up- and down-link.

For more, please see next page where we will intro the “Structure of the bidirectional OSA module”.

Notices: This article is reprinted from: opticsinfobase.org/oe/fulltext.cfm?uri=oe-22-2-1768&id=277085

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