A method and driving circuit for independently controlling average optical power and extinction ratio

Abstract

The present invention provides a method for independently controlling average optical power and extinction ratio by adding a compensation current source such that the current through the laser when the switch is on is I0 and the current through the laser when the switch is off is I1; and adjusting the size of the compensation current source such that I0+I1=2I UP , I UP is the bias current source size. The present invention also provides a circuit for independently controlling average optical power and extinction ratio.

Description

Technical Field

[0001] This invention belongs to the field of electronic circuits, and in particular to a laser driving circuit. Background Technology

[0002] like Figure 1 The figure shows the characteristic curves of the relationship between the laser input current and the laser output optical power. When the laser input current changes rapidly between I0 and I1, the range of change in the laser output optical power is P0 to P1. The average value of currents I0 and I1 is defined as the average operating current I of the laser. bias The difference between currents I1 and I0 is the laser modulation current I. mod =I1-I0; the laser output power corresponding to the average current is the average optical power Pav; the ratio of laser optical power P1 to P0 is the extinction ratio ER = 10logP1 / P0.

[0003] like Figure 2 This is a schematic diagram of a laser driver circuit. When the switch in the diagram is in the ON state, the current flowing through the laser is I0 = I UP -I DN When the switch is off, the current flowing through the laser is I1 = I UP Therefore, for the laser driving circuit shown in the figure, the average current I... bias =I UP -I DN / 2, Modulation current I mod =I DN Average current I bias Size not only with I UP Related to I DN Regarding adjusting the modulation current I of the laser. mod It will change the average current I of the laser. bias This makes it impossible to adjust the average optical power and extinction ratio of the laser separately, which brings certain inconvenience to the application.

[0004] In optical module applications consisting of a laser driver circuit and a laser, it is often desirable for a bias current I to flow into the laser. bias With modulation current I mod It can be intuitively and independently controlled, thus allowing for convenient control of the average optical power and extinction ratio of the laser emitted. Figure 2 The laser drive circuit adjusts the extinction ratio of the laser (i.e., adjusts I). mod When the current is applied, it will affect the average current I flowing into the laser. bias This affects the average optical power of the laser. Summary of the Invention

[0005] The main technical problem to be solved by this invention is to achieve the average current I flowing into the laser. bias With modulation current I mod The purpose is to be able to adjust independently and intuitively, and I bias with I mod They will not interfere with each other, thus achieving the goal of independent control of the laser's average optical power and extinction ratio.

[0006] To address the aforementioned technical problems, this invention provides a method for independently controlling average optical power and extinction ratio, characterized by: increasing a compensation current source so that when the switch is in the on state, the current flowing through the laser is I0, and when the switch is in the off state, the current flowing through the laser is I1; and adjusting the magnitude of the compensation current source so that I0 + I1 = 2I UP I UP This represents the magnitude of the bias current source.

[0007] In a preferred embodiment: the added compensation current source is I S When the switch is in the ON state, the current flowing through the laser is I0 = I UP -I DN +I S When the switch is off, the current flowing through the laser is I1 = I UP +I S ;

[0008] Then the average current I bias =(I0+I1) / 2=I UP -(I DN -2I S Let I = ) / 2 S =I DN / 2, then the average current I bias =I UP , where I DN For the magnitude of the modulated current source, I S To compensate for the size of the current source.

[0009] In a preferred embodiment: when the switch is in the ON state, the current flowing through the laser is I0 = I UP -I S When the switch is off, the current flowing through the laser is I1 = I UP +I S ;

[0010] Then I bias = (I0 + I1) / 2 = I UP -(I DN -I S Let I = ) / 2 DN =I S Then the average current Ibias =I UP , where I DN For the magnitude of the modulated current source, I S To compensate for the size of the current source.

[0011] The present invention provides a driving circuit for independently controlling the average optical power and extinction ratio, comprising: a bias current source and a modulation current source, and further comprising a compensation current source connected in parallel with the bias current source; the magnitude of the compensation current source is half that of the modulation current source.

[0012] The bias current source and the modulation current source are connected in series via a switch.

[0013] In a preferred embodiment: the modulation current source and the compensation current source are a single current source.

[0014] In a preferred embodiment: the modulation current source and the compensation current source are multiple sub-current sources connected in parallel.

[0015] In a preferred embodiment: the sub-current sources in the modulation current source and the compensation current source correspond one-to-one, and the size of the sub-current source in the compensation current source is half of the corresponding sub-current source in the modulation current source.

[0016] The present invention also provides a driving circuit for independently controlling the average optical power and extinction ratio, comprising: a bias current source and a modulation current source, and further comprising a compensation current source connected in parallel with the bias current source; the magnitude of the compensation current source is the same as that of the modulation current source.

[0017] The bias current source and the modulation current source are connected in series via a first switch, and the modulation current source and the compensation current source are connected in series via a second switch.

[0018] In a preferred embodiment: the modulation current source and the compensation current source are a single current source.

[0019] In a preferred embodiment: the modulation current source and the compensation current source are multiple sub-current sources connected in parallel.

[0020] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0021] This invention cancels the average current I by adding a current source. bias In the expression, I DN The components of the current, thus causing I bias =I UP This leads to the achievement of an average current I flowing into the laser. bias With modulation current I mod The laser's average optical power and extinction ratio can be independently and intuitively adjusted without affecting each other, thus achieving independent control of the laser's average optical power and extinction ratio. Attached Figure Description

[0022] Figure 1 This is a graph showing the relationship between the laser input current and the laser output optical power.

[0023] Figure 2 This is a schematic diagram of a laser driving circuit in the prior art;

[0024] Figure 3 This is a schematic diagram of a preferred embodiment 1 of the present invention;

[0025] Figure 4 This is a schematic diagram of a preferred embodiment 2 of the present invention;

[0026] Figure 5 This is a schematic diagram of a preferred embodiment 3 of the present invention;

[0027] Figure 6 This is a schematic diagram of preferred embodiment 4 of the present invention;

[0028] Figure 7 This is a schematic diagram of a preferred embodiment 5 of the present invention;

[0029] Figure 8 This is a schematic diagram of a preferred embodiment 6 of the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed", "equipped", "sleeved / connected", "connected", etc., should be interpreted broadly. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0033] This embodiment provides a method for independently controlling the average optical power and extinction ratio. This is achieved by adding a compensation current source so that when the switch is in the on state, the current flowing through the laser is I0, and when the switch is in the off state, the current flowing through the laser is I1; and by adjusting the magnitude of the compensation current source so that I0 + I1 = 2I... UP I UP This is the magnitude of the bias current source. This achieves the average current I flowing into the laser. bias With modulation current I DN The laser's average optical power and extinction ratio can be independently and intuitively adjusted without affecting each other, thus achieving independent control of the laser's average optical power and extinction ratio.

[0034] To implement the above method, this embodiment provides three specific circuits.

[0035] Example 1

[0036] refer to Figure 3 A driving circuit for independently controlling average optical power and extinction ratio includes: a bias current source and a modulation current source, and a compensation current source connected in parallel with the bias current source; the magnitude I of the compensation current source is... s Modulated current source I DN Half of it; the bias current source and the modulation current source are connected in series via a switch.

[0037] With the above design, when the switch is in the ON state, the current flowing through the laser is I0 = I UP -I DN +I S When the switch is off, the current flowing through the laser is I1 = I UP +I S ; then I bias = (I0 + I1) / 2 = I UP -

[0038] (I DN -2I S ) / 2, because I DN =2I S Then the average current I bias =IUP I UP This represents the magnitude of the bias current source.

[0039] Example 2

[0040] refer to Figure 4 The difference between this embodiment and Embodiment 1 is that the modulation current source I described in Embodiment 1... DN and compensation current source I s It is a single current source. However, in this embodiment, the modulated current source I... DN and compensation current source I s1 It consists of multiple sub-current sources connected in parallel. Furthermore, the modulated current source I... DN and compensation current source I s1 The sub-current sources in the diagram correspond one-to-one, and the compensation current source I... s The magnitude of the sub-current source in the modulation current source I is DN Half of the corresponding sub-current source.

[0041] After calculation, the average current I flowing into the laser is... bias =N*I P1 -1 / 2(Imod1+Imod2+…+Imodn), while I P1 =Ibiasp1 + Imod1 / 2N + Imod2 / 2N + ... + Imod2 / 2N, finally calculating I bias =N*I biasp1 Thus, the laser's I... bias Current and I mod The purpose of independent current control.

[0042] Example 3

[0043] refer to Figure 5 Add a compensation current source I S1 =I mod1 / 2N+I mod2 / 2N+…+I modn / 2N, after calculation, the average current I flowing into the laser is... bias =N*I P1 -1 / 2(I mod1 +I mod2 +…+I modn ), while I P1 =I biasp1 +I mod1 / 2N+I mod2 / 2N+…+I modn / 2N, therefore I bias =N*I biasp1 In this way, the goal of independently controlling the Ibias current and Imod current of the laser is achieved.

[0044] Example 4

[0045] refer to Figure 6 This embodiment provides a driving circuit for independently controlling the average optical power and extinction ratio, including: a bias current source I. P2 Compensating current source I S Switch Q1, switch Q2, load Z1, load Z2, and modulation current source I N2 The bias current source I P2 The upper end is connected to the power supply VDD, and the lower end is connected to the upper end of the load Z1; the compensation current source I S With bias current source I P2 The load Z1 is connected in parallel; the lower end of the load Z1 is connected to the upper end of the switch Q1; the lower end of the switch Q1 is connected to the modulation current source I. N2 The upper end of the load Z2 is connected to the lower end of the bias current source, and the lower end of the load Z2 is connected to the upper end of the switching transistor Q2; the lower end of the switching transistor Q2 is connected to the modulation current source I. N2 The upper end; Modulation current source I N2 The lower end of the transistor is grounded; the anode of the laser is connected to the upper end of the switch Q2, and the cathode is grounded; the switches Q1 and Q2 form a differential pair in the driving circuit, and the control terminals of the switches Q1 and Q2 are respectively connected to one end of the differential input signal and the other end. In this embodiment, the switches Q1 and Q2 are implemented using NPN transistors, but other devices (such as NMOS transistors) can also be used.

[0046] With the above design, when the input differential signal of the input differential pair transistors switches at high speed, the average current I flowing through the laser is... bias =I P2 +I S -I N2 By designing a compensation current source I S =I N2 Therefore I bias =I P2 Therefore, the bias current flowing through the laser is supplied by the bias current source I. P2 Controlled, the modulation current is controlled by the modulation current source I. N2 control.

[0047] Example 5

[0048] refer to Figure 7 The difference between this embodiment and embodiment 4 is that the current magnitude of the compensation current source is I. S2 =I N2 / N. The average current I of the laser has been calculated. bias =N*I biasp2 I mod =I N2Achieving the expected I bias with I mod The purpose of independent control is to achieve independent control of the average optical power and extinction ratio of the laser.

[0049] Example 6

[0050] refer to Figure 8 The magnitude of the current from the compensation current source in the diagram is I. S2 =I N2 / 2N. The average current I of the laser has been calculated. bias =N*I biasp2 I mod =I N2 Achieving the expected I bias with I mod The purpose of independent control.

[0051] The above description is merely a preferred embodiment of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention by those skilled in the art within the scope of the technology disclosed in the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A driving circuit for independently controlling average optical power and extinction ratio, characterized in that... include: The bias current source and the modulation current source also include a compensation current source connected in parallel with the bias current source; the magnitude of the compensation current source is half that of the modulation current source. The bias current source is connected to the power supply VDD at its upper end and to one end of the switch at its lower end; the other end of the switch is connected to the upper end of the modulation current source and the lower end of the modulation current source is grounded, so that the bias current source and the modulation current source are connected in series through the switch; one end of the compensation current source is connected to the power supply VDD and the other end is connected to the common node of the switch and the laser anode; the laser cathode is grounded; the modulation current source and the compensation current source are single current sources. By increasing the compensation current source so that the current flowing through the laser is I0 when the switch is in the on state and I1 when the switch is in the off state; and by adjusting the magnitude of the compensation current source so that I0 + I1 = 2I UP I UP This refers to the magnitude of the bias current source; When the switch is in the ON state, the current flowing through the laser is I0 = I UP -I DN +I S When the switch is off, the current flowing through the laser is I1 = I UP +I S ; Then the average current I bias =(I0+I1) / 2=I UP -(I DN -2I S Let I = ) / 2 DN =2I S Then the average current I bias =I UP , where I DN For the magnitude of the modulated current source, I S To compensate for the size of the current source.

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