Optical loopback circuits for transceivers and related methods

A method comprising:

• modulating, with a Mach-Zehnder optical modulator having first and second output terminals and disposed within a housing, a plurality of symbols onto an optical signal, wherein at least one symbol of the plurality of symbols represents a number of bits greater than one;
• transmitting a first portion of the optical signal outside the housing through the first output terminal of the Mach-Zehnder optical modulator, wherein transmitting the first portion of the optical signal outside the housing comprises transmitting the first portion of the optical signal through a first optical waveguide coupling the first output terminal of the Mach-Zehnder optical modulator to a fiber output port;
• and
• coupling a second portion of the optical signal from the second output terminal of the Mach-Zehnder optical modulator to an input terminal of an optical receiver disposed within the housing using an optical loopback circuit disposed within the housing, wherein coupling the second portion of the optical signal from the second output terminal of the Mach-Zehnder optical modulator to the input terminal of the optical receiver comprises transmitting the second portion of the optical signal through a second optical waveguide coupling the second output terminal of the Mach-Zehnder optical modulator to an optical switch of the optical loopback circuit.

An apparatus, comprising:

• a housing;
• and
• an optical transceiver disposed within the housing, the optical transceiver comprising:
• an optical transmitter having a first output terminal and a second output terminal, the optical transmitter being configured to transmit a plurality of symbols through the first output terminal, wherein at least one symbol of the plurality of symbols represents a number of bits greater than one;
• an optical receiver having a first input terminal and a second input terminal, the first input terminal of the optical receiver being connected to an optical fiber;
• a first optical waveguide and a second optical waveguide;
• and
• an optical loopback circuit coupling the second output terminal of the optical transmitter to the second input terminal of the optical receiver, wherein the optical loopback circuit comprises an optical switch,
• wherein the optical transmitter and optical receiver are disposed on separate substrates,
• wherein the first output terminal and the second output terminal of the optical transmitter are formed using respective output terminals of a Mach-Zehnder optical modulator configured to modulate the plurality of symbols onto an optical signal, and
• wherein the first optical waveguide couples the first output terminal of the optical transmitter to a fiber output port of the apparatus and wherein the second optical waveguide couples the second output terminal of the optical transmitter to the optical switch.