Compact optical sub-assembly
View Patent ↗The invention relates to a compact transmitter optical sub-assembly (OSA), which can be used in small form factor optical transceivers. To limit back reflections from entering the laser cavity, the laser is disposed on a silicon optical bench (SiOB) at an acute angle to the longitudinal axis of the OSA. A portion of the light from the laser cavity passes through the back end of the laser cavity for measuring by a monitor photodiode. A rear beam steering lens redirects the portion of light into a v-groove in the SiOB and off of a reflective surface formed in the end thereof to the monitor photodiode, which is positioned face down over the v-groove.
1. A transmitter optical sub-assembly, for converting an electrical data signal into an optical data signal, comprising:
a housing for supporting the transmitter optical sub-assembly defined by a width;
an optical coupler attached to the housing for receiving an optical fiber along a longitudinal optical axis;
a laser assembly including a laser and a modulator mounted in said housing, for generating light comprising the optical data signal, the laser for launching a beam light from a front face along a laser axis, which is at an acute angle to the longitudinal optical axis, and for releasing a portion of the light from a rear face along the laser axis;
an electrical connector for transmitting the electrical data signal from host electronics to the laser;
a front lensing means for directing the beam of light from the laser assembly to the optical coupler;
a monitor photo-detector for receiving the portion of the light from the rear face providing a signal indicative of the beam of light;
a rear beam steering lens for redirecting the portion of the light from the laser axis back towards the longitudinal optical axis, and for focusing the portion of the light onto the monitor photo-detector, thereby enabling the width of the housing to be reduced.
2. The TOSA according to claim 1 , wherein the rear beam steering lens redirects the portion of the light along or parallel to the longitudinal optical axis.
3. The TOSA according to claim 1 , further comprising an optical bench for supporting the laser, the rear beam steering lens, and the monitor photo-detector.
4. The TOSA according to claim 3 , wherein the rear beam steering lens redirects the portion of the light into a groove in the optical bench underneath the monitor photo-detector; wherein the groove includes a reflective surface for reflecting the portion of the light into the monitor photo-detector; and wherein the monitor photo-detector is mounted face down over the groove.
5. The TOSA according to claim 4 , wherein the monitor photo-detector is mounted face down over the groove in a junction up rear-illuminated fashion or a junction-down flip-chip fashion.
6. The TOSA according to claim 4 , wherein the housing is about 6 mm is width for mounting within industry standard small form factor transceivers.
7. The TOSA according to claim 3 , wherein the optical bench includes a first impedance matching resistor connected in parallel with a transmission line to the laser to match the impedance of the transmission line with that of the laser, and a second impedance matching resistor connected in series with the transmission line to the laser for reducing microwave reflection at frequencies greater than 5 GHz.
8. The TOSA according to claim 7 , wherein the second impedance matching resistors are electrically connected directly to the modulator.
9. The TOSA according to claim 7 , wherein the first impedance matching resistor is a thin film resistor in a co-planar transmission line integrated into the optical bench.
10. The TOSA according to claim 1 , wherein the electrical connector includes a multi-layer ceramic feed-through for bringing controlled impedance electrical data signals to the laser comprising:
spaced apart signal and ground traces extending from one side of the feed-through to another side between two of the ceramic layers;
a first ground plane positioned above the signal and ground traces with at least one ceramic layer with a first thickness therebetween;
a second round plane positioned below the signal and ground traces with at least one ceramic layer with a second thickness therebetween; and
conductive vias extending vertically through the ceramic layers above and below the signal and ground traces for electrically connecting the first ground plane, the ground traces, and the second ground plane;
whereby the spacing between the signal and ground traces, and the first and second thicknesses are selected to provide a desire impedance.
11. The TOSA according to claim 10 , wherein the electrical connector includes a flexible circuit attached to the ceramic feed-through including a conductive ground layer and a conductive signal layer for transmitting the electrical data and control signals along controlled impedance transmission lines.
12. The TOSA according to claim 1 , further comprising a thermal electric cooler to maintain the laser at a stable operating temperature.
13. The TOSA according to claim 1 , wherein the modulator redirects the beam of light from the laser axis to the longitudinal optical axis.
14. The TOSA according to claim 13 , wherein the front lensing means comprises a collimating lens adjacent the laser assembly for collimating the beam of light, and a focusing lens mounted in the housing for focusing the beam of light onto the optical fiber.
15. A transmitter optical sub-assembly, for converting an electrical data signal into an optical data signal, comprising:
a housing for supporting the transmitter optical sub-assembly defined by a width;
an optical coupler attached to the housing for receiving an optical fiber;
a laser assembly including a laser and a modulator mounted in said housing, for generating light comprising the optical data signal, the laser for launching a beam light from a front face along a laser axis, and for releasing a portion of the light from a rear face along the laser axis;
an electrical connector for transmitting the electrical data signal from host electronics to the laser;
a front lensing means for directing the beam of light from the laser assembly to the optical coupler;
a monitor photo-detector for receiving the portion of the light from the rear face providing a signal indicative of the beam of light;
a rear beam steering lens for redirecting the portion of the light from the laser axis to a photo-detector axis, which is at an acute angle to the laser axis, and for focusing the portion of the light onto the monitor photo-detector; and
an optical bench for supporting the laser, the rear beam steering lens, and the monitor photo-detector;
wherein the rear beam steering lens redirects the portion of the light into a groove in the optical bench underneath the monitor photo-detector;
wherein the groove includes a reflective surface for reflecting the portion of the light into the monitor photo-detector; and
wherein the monitor photo-detector is mounted face down over the groove.
16. The TOSA according to claim 15 , wherein the monitor photo-detector is mounted face down over the groove in a junction up rear-illuminated fashion or a junction-down flip-chip fashion.
17. A transmitter optical sub-assembly, for converting an electrical data signal into an optical data signal, comprising:
a housing for supporting the transmitter optical sub-assembly defined by a width;
an optical coupler attached to the housing for receiving an optical fiber;
a laser assembly including a laser and a modulator mounted in said housing, for generating light comprising the optical data signal, the laser for launching a beam light from a front face along a laser axis, and for releasing a portion of the light from a rear face along the laser axis;
an electrical connector for transmitting the electrical data signal from host electronics to the laser;
a front lensing means for directing the beam of light from the laser assembly to the optical coupler;
a monitor photo-detector for receiving the portion of the light from the rear face providing a signal indicative of the beam of light;
a rear beam steering lens for redirecting the portion of the light from the laser axis to a photo-detector axis, which is at an acute angle to the laser axis, and for focusing the portion of the light onto the monitor photo-detector; and
an optical bench for supporting the laser, the rear beam steering lens, and the monitor photodetector;
wherein the optical bench includes a first impedance matching resistor connected in parallel with a transmission line to the laser to match the impedance of the transmission line with that of the laser, and a second impedance matching resistor connected in series with the transmission line to the laser for reducing microwave reflection at frequencies greater than 5 GHz.
18. The TOSA according to claim 17 , wherein the first impedance matching resistor is a thin film resistor in a co-planar transmission line integrated into the optical bench.