Single-chip wavelength converter

Details Single-chip wavelength converter Single-chip wavelength converter

1999-06-08

2001-09-25

Lee, Eddie (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

Responsive to non-electrical signal

Electromagnetic or particle radiation

C257S021000, C257S080000, C385S014000

Reexamination Certificate

active

06294821

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to the field of optical communications and in particularly relates to an integrated optical wavelength converter fabricated on a single chip.
BACKGROUND OF THE INVENTION
Wavelength conversion and converters are well known in the art of communications and specifically as it relates to wavelength division multiplexed lightwave networks. In general, data carried on an incident light wave at a first wavelength &lgr;
1
may be transferred to a second light wave at &lgr;
2
, by modulating a continuous lightwave (“CW”) at &lgr;
2
.
Referring to
FIG. 1
an example of a prior art wavelength converter is shown. A light wave at &lgr;
1
is shown incident at a photodetector
10
, shown for purposes of illustration as a photodiode. The resulting electrical current output from detector
10
may pass through a pre-amplifier
20
such as shown, typically used to amplify the electrical signal to an intermediate level without degrading the signal to noise ratio of the signal. Thereafter, the signal is further amplified as it passes through amplifier
30
and followed by the last amplifier, also referred to as driver
40
. The output from driver
40
and CW light at &lgr;
2
are input to modulator
50
. Modulator
50
takes the electrical data from driver
40
, modulates the CW light at &lgr;
2
and outputs a lightwave at &lgr;
2
carrying the original incident data.
The amplification stage between detection and modulation is necessary because the incident signal may be at a low voltage level on the order of millivolts, while the modulator will typically require anywhere from 1-6 volts peak to peak. More specifically, a modulator such as
50
shown in
FIG. 1
may be manufactured from Lithium Niobate, in which case it will require 3 to 6 volts peak to peak. Alternatively, the modulator may be manufactured from semiconductor material in which case 1-3 volts should be sufficient. In either case, amplification is necessary.
The drawback of the wavelength converter of
FIG. 1
is that it includes electrical connections and devices. The electrical components are sensitive to data transmission rates and should have sufficient electrical bandwidth to operate at the data transmission rate. As bit rates increase, obtaining amplifiers with the proper bandwidth becomes a challenge. While connections can be fabricated to accept the higher bit rates, such as in the range of gigabytes, they must also be compatible with the amplifiers they inter-connect which traditionally have ratings of 50 ohms. Accordingly, in light of ever increasing demand for higher data transfer rates, it is desirable to reduce the constraints created by the electrical elements in the circuit, e.g. transistors, capacitors and wiring.
Referring to
FIG. 2
an alternative wavelength converter is shown which is known in the art as a Semiconductor Optical Amplifier (“SOA”). SOA
60
is a single semiconductor material whose properties allow for the amplification and modulation of an incident light wave into a second wavelength. SOA
60
accepts two inputs: the data at &lgr;
1
and the CW at &lgr;
2
. Direct current voltage is applied to the device and the data is output at an amplified level and at &lgr;
2
. The process of SOA
60
is also referred to as cross gain modulation and is more fully described in S. J. B. Yoo, “
Wavelength Conversion Technologies for WDM Network Applications
,” in 14 Journal of Lightwave Technology p. 955 (1996), hereby incorporated by reference as if fully set forth herein.
While for certain applications an SOA may be the device of choice, as compared with the opto/electronic wavelength converter of
FIG. 1
, it suffers certain drawbacks, including the introduction of certain non linear noise into the signal.
SUMMARY OF THE INVENTION
The subject invention addresses the inefficiencies and drawbacks identified above with respect to the prior art wavelength converters and introduces a new single-chip wavelength modulator without the electrical amplifier components found in the prior art. A high performance photodetector is integrated with a high performance modulator and a resistor on a single semiconductor substrate. DC biases are applied to each of the diodes of the photodetector and modulator. As light is incident on the photodetector a current is generated which causes a voltage drop across the resistor. The voltage across the modulator then becomes the difference between its DC bias and the voltage drop across the resistor. By properly selecting a resistor any desirable voltage swing can be achieved without electrical amplifiers. Furthermore, since the device is primarily optical and on a single semiconductor substrate the device is independent of data rate, subject only to the inherent timing constant of the circuit.


REFERENCES:
patent: 5063426 (1991-11-01), Chandrasekhar et al.
patent: 5577139 (1996-11-01), Chandrasekhar
patent: 5745271 (1998-04-01), Ford et al.
patent: 5991060 (1999-11-01), Fishman et al.
patent: JP-3-269226-A (1991-11-01), None
S.J.B. Yoo, “Wavelength Conversion Technologies for WDM Network Applications,” 14 Journal of Lightwave Technology p. 955 (Jun. 1996).
Thomas H. Wood, “Multiple Quantum Well (MQW) Waveguide Modulators,” 6 Journal of Lightwave Technology p. 743 (Jun. 1988).

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