Method & apparatus for optical transmission

• US 20030138024A1
• Filed: 01/15/2003
• Published: 07/24/2003
• Est. Priority Date: 12/22/1999
• Status: Abandoned Application

• Current Assignee: New Focus Inc. (MKS Instruments Incorporated)
• Original Assignee: New Focus Inc. (MKS Instruments Incorporated)
• Inventors: Rodwell, Mark, Williamson, Robert S. III, Marsland, Robert A.
• Application Number:
  US10/342,933
• Publication Number:
  US 20030138024A1
• Time in Patent Office: Days
• US Class Current: 372/108
• CPC Class Codes: G02B 6/4203 Optical features
• CPC Class Codes: H01L 2224/49171 Fan-out arrangements
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/1305 Bipolar Junction Transistor [BJT]
• CPC Class Codes: H01L 2924/3011 Impedance
• CPC Class Codes: H01L 2924/30111 matching
• CPC Class Codes: H01S 5/02216 Butterfly-type, i.e. with electrode pins extending horizontally from the housings
• CPC Class Codes: H01S 5/02251 using optical fibres
• CPC Class Codes: H01S 5/02257 using windows, e.g. specially adapted for back-reflecting light to a detector inside the housing
• CPC Class Codes: H01S 5/0231 Stems
• CPC Class Codes: H01S 5/0232 Lead-frames
• CPC Class Codes: H01S 5/02345 Wire-bonding
• CPC Class Codes: H01S 5/0683 by monitoring the optical output parameters

Abstract

The present invention provides a method and apparatus for transmission of optical communications. The present invention provides an optical transmitter which includes a control circuit to enhance the stability of output power levels, a modulator circuit with precise impedance matching for high frequency performance, and an optical coupling mechanism that relaxes the alignment tolerances between the laser and the fiber and decreases the sensitivity of the gain medium to feedback from devices coupled to the fiber. These features allow the transmitter to deliver an optical output beam which can be modulated over a wide range of frequencies, duty cycles and amplitudes with very precise definition of the rising and falling edges of the waveform. In combination these features result in an optical transmitter that may be fabricated with relatively low cost and a reduced form factor when compared with prior art optical transmitters.

In an embodiment of the invention a semiconductor laser transmitter is disclosed. The semiconductor laser transmitter includes: a gain medium, an optical fiber, and a reflector. The gain medium generates an emission along a path. The optical fiber includes a tip portion located in the path to optically couple with the emission. A reflector is located on the tip portion to limit an optical coupling efficiency of said gain medium with said optical fiber.

In an alternate embodiment of the invention a method for transmitting optical power is disclosed.

Claims

1. A semiconductor laser transmitter comprising:

a gain medium for generating an emission along a path;

an optical fiber with a tip portion located in the path to optically couple with the emission;

a reflector on the tip portion to limit an optical coupling efficiency of said gain medium with said optical fiber.

2. The semiconductor laser transmitter of claim 1, wherein said gain medium comprises at least one of:

a vertical cavity surface emitting laser, a diode laser and an external cavity laser.

3. The semiconductor laser transmitter of claim 1, wherein said optical fiber comprises one of:

a single mode fiber and a multi-mode fiber.

4. The semiconductor laser transmitter of claim 1, wherein the reflector further reduces a feedback of optical energy from said optical fiber to said gain medium.

5. The semiconductor laser transmitter of claim 1, wherein said reflector includes a material layer coupled with the tip portion.

6. The semiconductor laser transmitter of claim 5, wherein said material layer comprises at least one of:

titanium, platinum, gold and silver.

7. The semiconductor laser transmitter of claim 1, wherein the tip portion of said optical fiber further defines an optical lens for collimating the emission along said optical fiber.

8. The semiconductor laser transmitter of claim 7, wherein the optical lens defined by the tip portion includes at least one of:

a convex lens, a conical lens, a parabolic lens, a hyperbolic lens, a ball lens and a graded index of refraction lens.

9. The semiconductor laser transmitter of claim 1, further comprising:

a power control system electrically coupled to said gain medium and optically coupled with at least a portion of the emission reflected from said reflector to provide feedback for control of a power level of said gain medium.

10. The semiconductor laser transmitter of claim 1, wherein said power control system further comprises:

a photo detector responsive to emissions reflected from said reflector to generate a current.

11. The semiconductor laser transmitter of claim 10, wherein said power control system further comprises:

a current mirror delivering a fixed current to an output coupled to both said photo detector and to said gain medium to vary a power level of said gain medium inversely in relationship with the current generated by said photo detector to control an output power level of said gain medium.

12. The semiconductor laser transmitter of claim 1, further comprising:

a differential driver with a positive input, a negative input and an output and the output coupled to the gain medium, and the positive input and the negative input responsive to a differential information signal coupled thereto to vary a level of the emissions of the gain medium to correspond with said differential information signal.

13. A method for transmitting optical signals, and the method comprising the acts of:

generating an optical emission along a path;

coupling an optical fiber with said optical emission along the path;

reflecting a portion of the optical emission away from the path;

generating an difference signal corresponding to a difference between a power level of the reflected portion of the optical emission and a reference power level; and

varying a power level of the optical emission generated in said first act of generating to correspond with said difference signal generated in said second act of generating to control the power level of the optical emission.

14. The method for transmitting of claim 13, further comprising the acts of:

accepting a pair of signal inputs a difference of which corresponds to an information signal;

differencing said pair of signal inputs to obtain an output signal corresponding to said information signal;

modulating the power level of the optical emission to correspond with said output signal.