A photodetector circuit is disclosed. The photodetector circuit includes an optical input configured to receive a source optical signal for detection by the photodetector circuit, an optical waveguide for coupling the optical input and at least one side of a plurality of sides of a photodiode, wherein the optical waveguide is configured to generate a first optical signal and a second optical signal from the source optical signal, and the photodiode coupled to the first optical waveguide, where the photodiode is illuminated on the at least one side by the first and second optical signals at different locations on the photodiode, where the photodiode generates a photocurrent based on the first and second optical signals reducing photocurrent saturation. Providing a delay between the first and second optical signals reduces an out-of-band frequency response of the photodiode circuit.

An optical reception apparatus (1) of the present invention includes: a local oscillator (11) outputting local oscillation light (22); an optical mixer (12) receiving a multiplexed optical signal (21) and the local oscillation light, and selectively outputting an optical signal (23) corresponding to the wavelength of the local oscillation light from the multiplexed optical signal; a photoelectric converter (13) converting the optical signal (23) output from the optical mixer into an electric signal (24); a variable gain amplifier (15) amplifying the electric signal (24) to generate an output signal (25) whose output amplitude is amplified to a certain level; a gain control signal generating circuit (16) generating a gain control signal (26) for controlling the gain of the variable gain amplifier (15); and a monitor signal generating unit (17) generating a monitor signal (27) corresponding to the power of the optical signal (23) using the gain control signal (26).

Optical receivers and methods for tuning an operating point of an optical resonator, such as a Fabry-Perot etalon are disclosed. A free-space optical signal is received at an optical receiver and directed towards at least one beam splitter. After passing through the beam splitter, the optical signal is reflected off a surface of the optical resonator. The reflected signal is detected and utilized to tune the operating point of the optical resonator.

A method for receiving a modulated receive signal, with a transmission unit having a laser and an electro-absorption modulator. The received optical receive signal is directed towards the laser; due to the irradiance of the optical receive signal onto the laser, the optical frequency of the light radiated from the laser is adapted to and/or aligned with the optical frequency of the received optical receive signal; the light radiated from the laser and the optical receive signal received via the optical waveguide are overlapped in the electro-absorption modulator; the thus-created overlapping signal from the electro-absorption modulator is converted into an electrical receive signal, in particular into an electrical current signal; and a receive signal is provided which corresponds to the electrical receive signal or is derived from same.

An optical receiver is provided with: an optical reception circuit which receives wavelength multiplexed light including signal light, converts the signal light into an electrical signal by coherent detection of the signal light using local oscillation light, and outputs the power of the local oscillation light, the bit error rate of the signal light and the electrical signal; and a controller which monitors the power of the local oscillation light and the bit error rate, calculates the signal-to-noise ratio of the signal light on the basis of the power of the local oscillation light and the bit error rate, and finds the number of wavelengths of the wavelength multiplexed light and the power per wavelength of the signal light on the basis of the signal-to-noise ratio and the power of the local oscillation light.

An optical module includes: a casing; a printed circuit board (PCB) connected to a first side wall of the casing and configured to provide first electrical signals to an optical transmitter assembly; the optical transmitter assembly arranged in the casing and configured to convert the first electrical signals into first optical signals; an optical receiver adapter and an optical transmitter adapter arranged outside the casing and connected to a second side wall of the casing, wherein the optical transmitter adapter is configured to receive second optical signals; a first displacement prism arranged in the casing and configured to direct the second optical signals toward an optical receiver assembly; and the optical receiver assembly configured to convert the second optical signals into second electrical signals. At least one component of the optical receiver assembly is arranged in the casing.

Various embodiments of a monolithic transceiver are described, which may be fabricated on a semiconductor substrate. The monolithic transceiver includes a coherent receiver module (CRM), a coherent transmitter module (CTM), and a local oscillation splitter to feed a local oscillation to the CRM and the CTM with a tunable power ratio. The monolithic transceiver provides tunable responsivity by employing avalanche photodiodes (APDs) for opto-electrical conversion. The monolithic transceiver also employs a polarization beam rotator-splitter (PBRS) and a polarization beam rotator-combiner (PBRC) for supporting modulation schemes including polarization multiplexed quadrature amplitude modulation (PM-QAM) and polarization multiplexed quadrature phase shift keying (PM-QPSK).

In a coherent optical receiver device, the dynamic range considerably decreases in the case of selectively receiving the optical multiplexed signals by means of the wavelength of the local oscillator light, therefore, a coherent optical receiver device according to an exemplary aspect of the invention includes a coherent optical receiver receiving optical multiplexed signals in a lump in which signal light is multiplexed; a variable optical attenuator; a local oscillator connected to the coherent optical receiver; and a first controller controlling the variable optical attenuator by means of a first control signal based on an output signal of the coherent optical receiver; wherein the coherent optical receiver includes a 90-degree hybrid circuit, a photoelectric converter, and an impedance conversion amplifier, and selectively detects the signal light interfering with local oscillation light output by the local oscillator out of the optical multiplexed signals; and the variable optical attenuator is disposed in the optical path of the optical multiplexed signals in a stage preceding the photoelectric converter, inputs the optical multiplexed signals, and outputs them to the coherent optical receiver controlling the intensity of the optical multiplexed signals based on the first control signal.

A system for transmitting data over an optical communication path is configured to receive data to be encoded in a bitstream for transmission using an optical communication path and encodes the received data to obtain a bitstream. The system is further configured to determine that the bitstream includes a sequence of consecutive bits, and obtain a power level at which to transmit a portion of the bitstream based on a count of the consecutive bits in the sequence. The system may be configured to selectively activate a light source at a power level according to a modulation scheme to optically transmit the portion of the bitstream at the power level.

A reception device 20 is configured to include a separation means 21 and a plurality of optical reception means 22. Each optical reception means 22 further includes an optical/electrical conversion means 23, a reception coefficient computation means 24, and a band restoration means 25. The separation means 21 separates a multiplexed signal into which signals of respective channels to which spectral shaping that narrows bandwidth to less than or equal to a baud rate is applied as band narrowing filter processing on the transmission side, based on characteristics of a transmission line are multiplexed at spacings less than or equal to the baud rate. Each band restoration means 25 applies processing having inverse characteristics to those of the band narrowing filter processing to a reception signal, based on the band narrowing parameter acquired by the reception coefficient computation means 24 and thereby restores the band of the reception signal.