Demultiplexing with clocked optical receivers

Details Demultiplexing with clocked optical receivers Demultiplexing with clocked optical receivers

1997-07-02

2001-03-20

Hofsass, Jeffery (Department: 2632)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200, C359S199200, C359S199200, C341S054000

Reexamination Certificate

active

06204942

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates to optical demultiplexers and, more particularly, to the use of clocked receivers in an optical demultiplexer.
BACKGROUND OF THE INVENTION
Demultiplexing is a function often performed in lightwave communication networks and data links. With reference to
FIG. 1
there is shown a schematic diagram of a typical lightwave communication system receiver including a demultiplexer and preceding components. As shown, the demultiplexing function is commonly performed using an optical detector
101
, an analog-optical preamplifier
102
combined with post-amplification
103
, a clock-recovery and decision circuit
104
to obtain full digital levels at the multiplexed data rate, followed by a digital demultiplexing circuit
105
to extract the individual bit streams
106
.
The need for the higher-speed electronic components prior to the demultiplexer is a potential problem, because these components must perform at the data rate of the multiplexed bit stream, which could impose either a performance bottleneck or a cost barrier. The de-multiplexing function itself is typically performed by electronic latches clocked at the lower speeds of the constituent data streams. It is clear then, that the most demanding components of a demultiplexer are the high-speed receiver and amplification circuits that precede the demultiplexer block. Undesirably, such components are complex and expensive.
SUMMARY OF THE INVENTION
In accordance with the present invention, a simple and inexpensive optical demultiplexer based on photo-receivers is described. In one embodiment, the optical demultiplexer demultiplexes a received N channel multiplexed optical data signal, at a first data rate, into N signal data channels, where N is an integer >1. The multiplexed optical data signal and a clock signal are inputted to N receivers, each receiver demultiplexing a different one of the N signal data channels from the received multiplexed optical data signal. In another embodiment, a shared photodetector converts the received multiplexed optical data signal into a multiplexed data signal which is then used by all of the N receivers.
According to one aspect of the invention, a clock generating means generates N clock signals at the signal data channel rate for use by the N receivers, each of the N clock signals having a different time delay, relative to a first clock signal. An additional aspect provides that each of the N clock signals have a different time delay which is equal to M times 1/N of the clock period of the signal data channel rate, where M is an integer which is 1≦M≦N−1.
According to other aspects of the invention, N clock signals may be generated using a voltage controlled delay line or using N−1 serially connected delay circuits each having a delay equal to 1/N of the clock period of the signal at channel rate. According to another aspect of the invention, at least one of the N optical receivers is a clocked sense-amplified-based photo-receiver. The clocked sense-amplified-based photo-receiver may also be implemented using CMOS technology. Additionally, the components of the optical demultiplexer may be integrated together on an integrated circuit chip.


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