Optical transmitter having pre-modulation amplification

• US 6,023,362 A
• Filed: 05/08/1997
• Issued: 02/08/2000
• Est. Priority Date: 05/08/1997
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Willems, Frederik Willem, Walker, Kenneth Lee
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US08/853,135
• Time in Patent Office: 1,006 Days
• Field of Search: 359/180, 359/181, 359/188, 359/156, 359/173, 372/26, 372/27
• US Class Current: 398/184
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H04B 10/505 using external modulation
• CPC Class Codes: H04B 10/564 Power control

Abstract

In one embodiment, an optical transmitter, which has a modulator disposed between an pair of optical amplifiers, exhibits reduced carrier-to-noise ratio and relatively high powers. In another embodiment, an optical amplifier is disposed between the laser carrier source and the modulator, but the post-modulator amplifier is omitted. Application of the transmitters to analog systems (e.g., CATV) and digital systems is described.

Claims

1. An optical transmitter comprising

an optical source of a first signal,

an optical modulator for impressing information on said first signal, thereby generating a modulated second signal, and

a post-modulation optical amplifier for amplifying said second signal, characterized in that said transmitter further includes

a pre-modulation optical amplifier for amplifying said first signal before it is applied to said modulator, wherein the gain of said pre-modulation amplifier is greater than unity and less than the level at which the carrier-to-noise ratio of said transmitter saturates.

2. The invention of claim 1 wherein said modulator is a polarization dependent modulator and said pre-modulation amplifier is a polarization-maintaining amplifier.

3. The invention of claim 2 wherein said modulator comprises a lithium niobate electro-optic modulator.

4. The invention of claim 1 wherein said modulator is a polarization dependent modulator and a polarization controller is disposed between said pre-modulation amplifier and said modulator.

5. The invention of claim 4 wherein said modulator comprises a lithium niobate electro-optic modulator.

6. The invention of claim 1 wherein said modulator comprises an analog modulator.

7. The invention of claim 1 wherein said source comprises a laser which generates a CW first signal having a linewidth less than about 300 MHz.

8. The invention of claim 7 wherein said laser generates said CW first signal having a linewidth less than about 5 MHz.

9. An optical transmitter comprising

a laser source for generating a CW carrier signal having a linewidth less than about 300 MHz,

an optical modulator for impressing analog information onto said carrier signal,

a post-modulation amplifier for amplifying said modulated carrier signal, and

a pre-modulation amplifier for amplifying said carrier signal before it is applied to said modulator,

the gain of said pre-modulation amplifier being greater than unity and less than the level where the carrier-to-noise ratio of said transmitter saturates.

10. The invention of claim 9 wherein said modulator comprises a polarization dependent modulator, said source generates said carrier signal as a polarized signal matched to the polarization of said modulator, and said pre-modulation amplifier comprises a polarization-maintaining amplifier.

11. The invention of claim 9 wherein said modulator comprises a polarization dependent modulator, said source generates said carrier signal as a polarized signal matched to the polarization of said modulator, and further including a polarization controller disposed between said pre-modulation amplifier and said modulator.

12. The invention of claim 9 wherein said laser source generates said CW carrier signal having a linewidth less that about 5 MHz.

13. An optical transmitter comprising

a laser source for generating a CW carrier signal having a linewidth less than about 300 MHz, and

an optical modulator for impressing information on said carrier signal, thereby generating a modulated second signal, characterized in that said transmitter further includes

a pre-modulation optical amplifier for amplifying said carrier signal before it is applied to said modulator, wherein the gain of said pre-modulation amplifier is greater than unity and less than the level at which the carrier-to-noise ratio of said transmitter saturates.

14. The invention of claim 13 wherein said laser source generates said CW carrier signal having a linewidth less than about 5 MHz.