# US 12,009,635 B2 · Switching circuit for burst-mode tunable laser

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- Number: US 12,009,635 B2
- Document ID: US12009635B2
- Status: Granted
- Kind: B2
- Application number: 17/057,649
- Filed: 2019-05-07
- Published: 2021-06-03
- Granted: 2024-06-11
- Earliest claimed: 2018-05-21
- Assignees: Google Inc.
- Applicants: Google LLC
- Inventors: Tao Zhang; Cedric Fung Lam; Xiangjun Zhao; Shuang Yin; Liang Du; Changhong Joy Jiang; Adam Edwin Taylor Ward Barratt; Claudio Desanti; Muthu Nagarajan
- Web page: https://patentgrep.com/patent/US12009635B2

## CPC

- H01S 5/0428: {for applying pulses to the laser}
- H01S 5/06256: {with DBR-structure}
- H01S 5/02415: {by using a thermo-electric cooler [TEC], e.g. Peltier element}
- H04B 10/504: {using direct modulation}
- H04B 10/572: Wavelength control
- H04J 14/0282: {WDM tree architectures}
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H04B: TRANSMISSION
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)

## Abstract

A method (600) for tuning a tunable laser (310) includes delivering a bias current (IDBR) to an anode of a distributed Bragg reflector (DBR) section diode (D2) disposed on a shared substrate of the tunable laser and receiving a burst mode signal (440) indicative of a burst-on state or a burst-off state. When the burst mode signal is indicative of the burst-off state, the method includes offsetting the bias current at the anode of the DBR section diode by one of sourcing a push current with the bias current to the anode of the DBR section diode or sinking a pull current away from the bias current at the anode of the DBR section diode. When the burst mode signal is indicative of the burst-on state, the method also includes ceasing any offsetting of the bias current at the anode of the DBR section diode.

## Claims

### Claim 1

A method for tuning a tunable laser, the method comprising:
delivering, by a switching circuit, a bias current to an anode of a distributed Bragg reflector (DBR) section diode disposed on a shared substrate of the tunable laser;
receiving, at the switching circuit, a burst mode signal indicative of a burst-on state or a burst-off state;
when the burst mode signal is indicative of the burst-off state, offsetting, by the switching circuit, the bias current at the anode of the DBR section diode by one of:
sourcing a push current with the bias current to the anode of the DBR section diode; or
sinking a pull current away from the bias current at the anode of the DBR section diode; and
when the burst mode signal is indicative of the burst-on state, ceasing, by the switching circuit, any offsetting of the bias current at the anode of the DBR section diode,
wherein, when the burst mode signal is indicative of the burst-off state, the DBR section diode receives a diode current equal to a sum of the bias current and a difference between a source current that sources current to the anode of the DBR section diode and a sink current that sinks current away from the bias current at the anode of the DBR section diode.

### Claim 2 (depends on 1)

The method of claim 1, wherein:
the bias current at the anode of the DBR section diode causes the tunable laser to transmit on a first channel associated with a working wavelength when the burst mode signal is indicative of the burst-on state; and
the offsetting of the bias current at the anode of the DBR section diode causes the tunable laser to transmit on a second channel adjacent to the first channel when the burst mode signal is indicative of the burst-off state, the second channel associated with a standby wavelength.

### Claim 3 (depends on 2)

The method of claim 2, wherein:
the standby wavelength is greater than the working wavelength when the bias current at the anode of the DBR section diode is offset by sourcing the push current with the bias current; and
the standby wavelength is less than the working wavelength when the bias current at the anode of the DBR section diode is offset by sinking the pull current away from the bias current.

### Claim 4 (depends on 1)

The method of claim 1, wherein, when the burst mode signal is indicative of the burst-off state and the source current is greater than the sink current, the bias current is offset by the sourcing of the push current with a magnitude equal to the difference between the source current and the sink current.

### Claim 5 (depends on 1)

The method of claim 1, wherein, when the burst mode signal is indicative of the burst-off state and the source current is less than the sink current, the bias current is offset by the sinking of the pull current from the bias current by a magnitude equal to the difference between the source current and the sink current.

### Claim 6 (depends on 1)

The method of claim 1, wherein, when the burst mode signal is indicative of the burst-on state, the DBR section diode receives a diode current equal to the bias current.

### Claim 7 (depends on 1)

The method of claim 1, further comprising, when the burst mode signal is indicative of the burst-off state:
receiving, at the switching circuit, a sink current from a current pull stage of the switching circuit that sinks current away from the bias current at the anode of the DBR section diode; and
receiving, at the switching circuit, a source current from a current push stage of the switching circuit that sources current to the anode of the DBR section diode.

### Claim 8 (depends on 7)

The method of claim 7, wherein the current pull stage comprises a differential pair of first and second transistors, each transistor connected to a burst mode signal source, the first transistor connected to a first inductor and a resistor, the resistor connected to a voltage source, the second transistor connected to a second inductor, the second inductor connected to the anode of the DBR section diode.

### Claim 9 (depends on 8)

The method of claim 8, wherein the first transistor is turned off and the second transistor is turned on to sink the sink current away from the anode of the DBR section diode when the burst mode signal is indicative of the burst-off state.

### Claim 10 (depends on 8)

The method of claim 8, wherein the first transistor is turned on and the second transistor is turned off to sink current across the resistor, the first inductor, and the first transistor from the voltage source connected to the resistor when the burst mode signal is indicative of the burst-on state.

### Claim 11 (depends on 7)

The method of claim 7, wherein the current push stage comprises a differential pair of first and second transistors, each transistor connected to a burst mode signal source and a voltage source, the first transistor connected to a first inductor and a resistor, the resistor connected to ground, the second transistor connected to a second inductor, the second inductor connected to the anode of the DBR section diode.

### Claim 12 (depends on 11)

The method of claim 11, wherein the first transistor is turned off and the second transistor is turned on to source the source current to the anode of the DBR section diode when the burst mode signal is indicative of the burst-off state.

### Claim 13 (depends on 11)

The method of claim 11, wherein the first transistor is turned on and the second transistor is turned off to draw the source current across the first transistor and through the first inductor and the resistor to the ground.

### Claim 14

A switching circuit for tuning a tunable laser, the switching circuit comprising:
a voltage source configured to deliver a bias current to an anode of a DBR section diode disposed on a shared substrate of the tunable laser;
a current controller configured to receive a burst mode signal indicative of a burst-on state or a burst-off state, the current controller configured to:
when the burst mode signal is indicative of the burst-off state, offset the bias current at the anode of the DBR section diode by one of:
sourcing a push current with the bias current to the anode of the DBR section diode; or
sinking a pull current away from the bias current at the anode of the DBR section diode; and
when the burst mode signal is indicative of the burst-on state, cease any offsetting of the bias current at the anode of the DBR section diode,
when the burst mode signal is indicative of the burst-off state, the DBR section diode receives a diode current equal to a sum of the bias current and a difference between a source current that sources current to the anode of the DBR section diode and a sink current that sinks current away from the bias current at the anode of the DBR section diode.

### Claim 15 (depends on 14)

The switching circuit of claim 14, wherein:
the bias current at the anode of the DBR section diode causes the tunable laser to transmit on a first channel associated with a working wavelength when the burst mode signal is indicative of the burst-on state; and
the offsetting of the bias current at the anode of the DBR section diode causes the tunable laser to transmit on a second channel adjacent to the first channel when the burst mode signal is indicative of the burst-off state, the second channel associated with a standby wavelength.

### Claim 16 (depends on 15)

The switching circuit of claim 15, wherein:
the standby wavelength is greater than the working wavelength when the bias current at the anode of the DBR section diode is offset by sourcing the push current with the bias current; and
the standby wavelength is less than the working wavelength when the bias current at the anode of the DBR section diode is offset by sinking the pull current away from the bias current.

### Claim 17 (depends on 14)

The switching circuit of claim 14, wherein, when the burst mode signal is indicative of the burst-off state and the source current is greater than the sink current, the bias current is offset by the sourcing of the push current with a magnitude equal to the difference between the source current and the sink current.

### Claim 18 (depends on 14)

The switching circuit of claim 14, wherein, when the burst mode signal is indicative of the burst-off state and the source current is less than the sink current, the bias current is offset by the sinking of the pull current from the bias current by a magnitude equal to the difference between the source current and the sink current.

### Claim 19 (depends on 14)

The switching circuit of claim 14, wherein, when the burst mode signal is indicative of the burst-on state, the DBR section diode receives a diode current equal to the bias current.

### Claim 20 (depends on 14)

The switching circuit of claim 14, further comprising:
a current pull stage configured to sink a sink current away from the bias current at the anode of the DBR section diode when the burst mode signal is indicative of the burst-off state; and
a current push stage configured to source a source current to the anode of the DBR section diode when the burst mode signal is indicative of the burst-off state.

### Claim 21 (depends on 20)

The switching circuit of claim 20, wherein the current pull stage comprises a differential pair of first and second transistors, each transistor connected to a burst mode signal source, the first transistor connected to a first inductor and a resistor, the resistor connected to a voltage source, the second transistor connected to a second inductor, the second inductor connected to the anode of the DBR section diode.

### Claim 22 (depends on 21)

The switching circuit of claim 21, wherein the first transistor is turned off and the second transistor is turned on to sink the sink current away from the anode of the DBR section diode when the burst mode signal is indicative of the burst-off state.

### Claim 23 (depends on 21)

The switching circuit of claim 21, wherein the first transistor is turned on and the second transistor is turned off to sink current across the resistor, the first inductor, and the first transistor from the voltage source connected to the resistor when the burst mode signal is indicative of the burst-on state.

### Claim 24 (depends on 20)

The switching circuit of claim 20, wherein the current push stage comprises a differential pair of first and second transistors, each transistor connected to a burst mode signal source and a voltage source, the first transistor connected to a first inductor and a resistor, the resistor connected to ground, the second transistor connected to a second inductor, the second inductor connected to the anode of the DBR section diode.

### Claim 25 (depends on 24)

The switching circuit of claim 24, wherein the first transistor is turned off and the second transistor is turned on to source the source current to the anode of the DBR section diode when the burst mode signal is indicative of the burst-off state.

### Claim 26 (depends on 24)

The switching circuit of claim 24, wherein the first transistor is turned on and the second transistor is turned off to draw the source current across the first transistor and through the first inductor and the resistor to the ground.